Determination of concentrations and amounts of perfluoroalkyl substances by lc/ms/ms

ABSTRACT

A method and system for injecting an unconcentrated sample into a receiving LC/MS/MS system that is configured to determine a concentration of one or more PFAS analytes within the unconcentrated sample, wherein the LC/MS/MS includes ESI. The unconcentrated sample may be subjected to one or more of the following ESI conditions: i) a probe gas temperature of approximately 120° C. to approximately 180° C.; ii) a sheath gas heater setting of approximately 250° C. to approximately 400° C.; and/or iii) a sheath gas flow of approximately 8 L/min to approximately 12 L/min. The unconcentrated sample&#39;s concentration and/or an injected amount of the one or more PFAS analytes is determined.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/708,812 filed on Dec. 10, 2019. The entire disclosure of the priorapplication is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate to qualitative andquantitative analysis of analytes in samples and more particularly tothe qualitative and quantitative analysis of perfluoroalkyl substancesin water.

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a group of man-madechemicals that includes perfluorooctanoic acid along with its conjugatebase perfluorooctanoate (PFOA) and perfluorooctanesulfonic acid alongwith its conjugate base perfluorooctanesulfonate (PFOS), as well as manyother chemicals. PFAS have been manufactured and used in a variety ofindustries around the globe since the 1940s. In general, PFAS are notreadily degraded by natural means, e.g., metabolism, due to their highlyfluorinated structures. Thus, PFAS accumulate over time in nature aswell as in living tissues. There is evidence that exposure to PFAS canlead to adverse human health effects.

Because of their widespread industrial usage, PFOA and PFOS are the moststudied PFAS. Studies indicate that PFOA and PFOS can cause reproductiveand developmental, liver and kidney, and immunological effects inlaboratory animals. Both chemicals have caused tumors in animals. Themost consistent findings are increased cholesterol levels among exposedpopulations. PFOA and PFOS exposure has been attributed to low infantbirth weights, effects on the immune system, cancer (for PFOA), andthyroid hormone disruption (for PFOS).

Recently, PFOA has been detected in the Hoosic River near Hoosick Falls,N.Y., presumably originating from a plant upstream from Hoosick Falls.Events such as this have triggered significant interest in findinginexpensive and sensitive methods for detecting PFAS such as PFOA andPFOS in other public water sources that are near plants that producePFAS.

SUMMARY OF INVENTION

Shortcomings of the prior art are overcome and additional advantages areprovided through the provision of methods and a system for detectingPFAS analytes and a PFAS analyte detection system for detecting one ormore PFAS analytes of formula C_(n)F(2n+1)—X in a solution and/or anunconcentrated sample, wherein n is 3, 4, 5, 6, 7, 8 or 9, and wherein—X is —SO3H, —CO2H, —SO3—, or —CO2-.

In a first aspect, a method is provided for facilitating detecting PFASanalytes that comprises injecting a solution and/or unconcentratedsample into a receiving LC/MS/MS (liquid chromatography/tandem massspectroscopy) system, which is configured to determine concentrations ofone or more PFAS analytes of formula C_(n)F(2n+1)—X within the solutionand/or unconcentrated sample, wherein the LC/MS/MS includes electrosprayionization (ESI); subjecting the solution and/or unconcentrated sampleto the following ESI conditions: i) a probe gas temperature ofapproximately 120° C. to approximately 180° C., ii) a sheath gas heatersetting of approximately 250° C. to approximately 400° C., and iii) asheath gas flow of approximately 8 L/min to approximately 12 L/min; anddetermining one or both of: i) a concentration of at least one of theone or more PFAS analytes within the unconcentrated sample, wherein theconcentration of the at least one PFAS analyte is between approximately0.0020 μg/L and approximately 0.25 μg/L; and ii) an amount of at leastone of the one or more PFAS analytes within the injected volume of theunconcentrated sample, wherein the amount of the at least one PFASanalyte is between approximately 1.5×10-7 μg and approximately 1.9×10⁻⁵μg.

In a second aspect, a PFAS analyte detection system is provided for thatcomprises an LC/MS/MS system operable utilizing ESI and configured to:receive an injected volume of the solution and/or unconcentrated sample;subject the injected volume of the unconcentrated sample to ESIconditions as follows: i) a probe gas temperature of approximately 120°C. to approximately 180° C., ii) a sheath gas heater setting ofapproximately 250° C. to approximately 400° C., and iii) a sheath gasflow of approximately 8 L/min to approximately 12 L/min; and determineone or both of: i) a concentrations of at least one of the one or morePFAS analytes within the unconcentrated sample, wherein theconcentration of the at least one PFAS analyte is between approximately0.0020 μg/L and approximately 0.25 μg/L and ii) an amount of at leastone of the one or more PFAS analytes within the injected volume of theunconcentrated sample, wherein the amount of the at least one PFASanalyte is between approximately 1.5×10-7 μg and approximately 1.9×10⁻⁵μg.

In a third aspect, a method is provided for facilitating detecting PFASanalytes that comprises:

obtaining an unconcentrated sample containing one or more PFAS analytesof formula C_(n)F(2n+1)—X as described above;

receiving data representative of test results of an analysis of aconcentration and/or amount of at least one of the one or more PFASanalytes of formula C_(n)F(2n+1)—X within at least a portion of theunconcentrated sample, wherein the test results comprising one or both:

-   -   i) the concentration of the at least one PFAS analyte in the        unconcentrated sample; and    -   ii) the amount within an injected volume of the unconcentrated        sample of the at least one PFAS analyte into an LC/MS/MS system;        and wherein the analysis comprised the following steps a) and        b):    -   a) injecting a volume of the unconcentrated sample into the        LC/MS/MS system with ESI that is configured to determine the        concentration of the at least one PFAS analyte; and    -   b) subjecting the injected volume of the unconcentrated sample        to ESI conditions as follows:    -   i) a probe gas temperature of approximately 120° C. to        approximately 180° C.;    -   ii) a sheath gas heater setting of approximately 250° C. to        approximately 400° C.; and    -   iii) a sheath gas flow of approximately 8 L/min to approximately        12 L/min.

In an embodiment, the method and systems further comprises: i) theconcentration of the at least one PFAS analyte within the solutionand/or unconcentrated sample is between approximately 0.010 μg/L andapproximately 0.25 μg/L; and/or ii) the amount of the at least one PFASanalyte within the injected volume of the unconcentrated sample isbetween approximately 7.5×10-7 μg and approximately 1.9×10⁻⁵ μg.

In an embodiment, the method and systems further comprises subjectingthe solution and/or unconcentrated sample to the following ESIconditions: i) a gas flow setting of between approximately 11 L/min toapproximately 20 L/min; and ii) a capillary voltage setting of betweenapproximately 1500 V to approximately 4000 V.

In an embodiment, the method and systems further comprises subjectingthe solution and/or unconcentrated sample to the following ESIconditions: i) a gas flow setting of between approximately 11 L/min toapproximately 20 L/min; and ii) a capillary voltage setting of betweenapproximately 1500 V to approximately 4000 V.

In an embodiment, the method and systems further comprises subjectingthe solution and/or unconcentrated sample to the following ESIconditions: i) a probe gas temperature of approximately 120° C.; ii) asheath gas heater setting of approximately 400° C.; and iii) a sheathgas flow of approximately 8 L/min.

In an embodiment, the method and systems further comprises subjectingthe solution and/or unconcentrated sample to the following ESIconditions: i) a gas flow setting of approximately 11 L/min; and ii) acapillary voltage setting of approximately 1500 V.

In an embodiment, the method and systems further comprises the one ormore PFAS analytes of formula C_(n)F(2n+1)—X are chosen from: PFBA,PFBS, PFDA, PFHpA, PFHpS, PFHxA, PFHxS, PFNA, PFPeS, PFOA, and PFOS.

In an embodiment, the unconcentrated sample and/or solution are aqueousunconcentrated samples and/or solutions. In this embodiment, the aqueousunconcentrated samples and/or solutions are selected from: finisheddrinking water, ground water, raw source water, and water at anintermediate stage of treatment between raw source water and finisheddrinking water. Further, the unconcentrated sample and/or solution maycontain analytes other than PFAS such as impurities from the watersource, preservatives, buffers, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of components of an LC/MS/MS system usedto determine concentrations and amounts of PFAS analytes in solutionsand/or unconcentrated samples, in accordance with an exemplaryembodiment of the present invention.

FIG. 2 illustrates processes for validating a method to determineconcentrations and amounts of PFAS analytes in solutions and/orunconcentrated samples, in accordance with an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION

Currently, the quantitative determination of low levels of the PFASanalytes in water sources often requires extraction of the PFAS analytesfrom the water. This requirement is typically due to the limitations ofthe analytical methods employed for sample analysis. When analyteconcentrations are too low to be quantitated by established analyticaltechniques, extraction thereof serves to provide a more concentratedsample than the originally collected unconcentrated water sample. Theseextraction steps are often time-consuming, costly, and inherentlyintroduce the possibility of errors in the analysis along with anincrease in possible sample contamination. In some cases, up to oneliter of water from a contaminated water source must be extracted toprovide 1 mL of an aqueous sample after evaporation of extractingsolvent and subsequent aqueous dissolution of the isolated extract.

Embodiments of the present invention recognize that extraction stepscontribute to increased costs and errors in the qualitative andquantitative analysis of PFAS analytes in water samples. Embodiments ofthe present invention provide a method and LC/MS/MS system for thedetermination of concentrations and amounts of low levels of PFASanalytes in unconcentrated as well as concentrated samples. Thus,extraction techniques may be avoided in the analysis of PFAS analytes inunconcentrated samples, such as finished drinking water, ground water,raw source water, and water at an intermediate stage of treatmentbetween raw source water and finished drinking water.

As described herein, “PFAS analyte” indicates a poly- or perfluorinatedalkyl carboxylic or sulfonic acid and/or the corresponding conjugatebases. It will be readily understood by one having ordinary skill in theart that the relative quantity of the acid and conjugate base will bedependent on the pH of the sample and/or standard that contains the PFASanalyte as well as the pKa (H2O) of the PFAS acid component within thegiven sample and/or standard solution.

The PFAS analytes, as acids and/or the corresponding conjugate bases,that are detected in a solution or an unconcentrated sample includewithout limitation: i) perfluorobutanoic acid (C3F7CO2H) and/or theconjugate base thereof, i.e., perfluorobutanoate (C3F7CO2-); ii)perfluorobutanesulfonic acid (C4F9SO3H) and/or the conjugate basethereof, i.e., perfluorobutane sulfonate (C4F9SO3-); iii)perfluoropentanesulfonic acid (C5F11SO3H) and/or the conjugate basethereof, i.e., perfluoropentane sulfonate (C5F11SO3-); iv)perfluorohexanoic acid (C5F11CO2H) and/or the conjugate base thereof,i.e., perfluorohexanoate (C5F11CO2-); v) perfluorohexanesulfonic acid(C6F13SO3H) and/or the conjugate base thereof, i.e., perfluorohexanesulfonate (C6F13SO3-); vi) perfluoroheptanoic acid (C6F13CO2H) and/orthe conjugate base thereof, i.e., perfluoroheptanoate (C6F13CO2-); vii)perfluoroheptanesulfonic acid (C7F15SO3H) and/or the conjugate basethereof, i.e., perfluoroheptane sulfonate (C7F15SO3-); viii)perfluorooctanoic acid (C7F15CO2H) and/or the conjugate base thereof,i.e., perfluorooctanoate (C7F15CO2-); ix) perfluorooctanesulfonic acid(C8F17SO3H) and/or the conjugate base thereof, i.e., perfluorooctanesulfonate (C8F17SO3-); x) perfluorononanoic acid (C8F17CO2H) and/or theconjugate base thereof, i.e., perfluorononanoate (C8F17CO2-); and xi)perfluorodecanoic acid (C9F19CO2H) and/or the conjugate base thereof,i.e., perfluorodecanoate (C9F19CO2-).

The method and system encompasses the concentration determination of, ina solution or an unconcentrated sample, all known isomers of PNASanalytes with the general formula C_(n)F(2n+1)—X as described herein.

PFAS analyte acronyms used throughout this description are as shown inTable 1.

TABLE 1 Acronym Definitions. Analyte Name (Acid/Conjugate Base) AcronymPerfluorobutanoic acid/Perfluorobutanoate PFBA Perfluorobutanesulfonicacid/Perfluorobutane sulfonate PFBS Perfluorodecanoicacid/Perfluorodecanoate PFDA Perfluoroheptanoic acid/PerfluoroheptanoatePFHpA Perfluoroheptanesulfonic acid/Perfloroheptanesulfonate PFHpSPerfluorohexanoic acid/Perfluorohexanoate PFHxA Perfluorohexanesulfonicacid/Perflorohexanesulfonate PFHxS Perfluorononanoicacid/Perfluorononanoate PFNA Perfluoropentanesulfonicacid/Perfloropentanesulfonate PFPeS Perfluorooctanoicacid/Perfluorooctanoate PFOA Perfluorooctanesulfonicacid/Perflorooctanesulfonate PFOS

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function, anduse of the methods and systems disclosed herein. One or more examples ofthese embodiments are illustrated in the accompanying drawings. Thoseskilled in the art will understand that the methods and systemsspecifically described herein and illustrated in the accompanyingdrawings are non-limiting exemplary embodiments and that the scope ofthe present invention is defined solely by the claims. The featuresillustrated or described in connection with one exemplary embodiment maybe combined with the features of other embodiments. Such modificationsand variations are intended to be included within the scope of thepresent invention.

The terms “substantially”, “approximately”, “about”, “relatively,” orother such similar terms that may be used throughout this disclosure,including the claims, are used to describe and account for smallfluctuations, such as due to variations in processing. For example, theycan refer to less than or equal to ±10%, such as less than or equal to±5%, such as less than or equal to ±2%, such as less than or equal to±1%, such as less than or equal to ±0.5%, such as less than or equal to±0.2%, such as less than or equal to ±0.1%, such as less than or equalto ±0.05%.

The ranges disclosed herein include increments governed by significantfigures as recited in the ranges. For example, a temperature range ofapproximately 120° C. to approximately 125° C. indicates threesignificant figures, hence approximately 120 to approximately 121° C.,approximately 121 to approximately 122° C., approximately 122 toapproximately 123° C., approximately 123 to approximately 124° C., andapproximately 124 to approximately 125° C. are thereby included as rangesubsets.

In various embodiments, unconcentrated samples are analyzed fordetection and quantitation of PFAS analytes. As used herein,“unconcentrated sample” typically refers to an aqueous sample collectedfrom a water source such as, but not limited to, finished drinkingwater, ground water, raw source water, and water at an intermediatestage of treatment between raw source water and finished drinking water.The sample may also be collected from an effluent from processes thatutilize one or more PFAS analytes, such as from a factory that producesPFAS-containing products. The unconcentrated sample is not concentratedby any deliberate or substantial evaporation of the solvent, i.e.,water. Further, the unconcentrated sample is not concentrated by, forexample, extraction into an organic solvent to subsequently make anon-aqueous or aqueous solution of PFAS analyte(s) that have higherconcentrations than the originally collected sample. An unconcentratedsample also includes a sample that is diluted with respect to theoriginally collected sample. The diluent may be water or awater-miscible solvent such as, but not limited to, an alcohol (e.g.,methanol, ethanol, n-propanol, isopropanol, n-butanol sec-butanol,iso-butyl alcohol, tert-butyl alcohol, diols such as ethylene glycol,triols such as glycerol, etc.), acetonitrile, etc. In some embodiments,unconcentrated samples also contain added chemicals, such as ammoniumchloride, buffers, etc., for purposes of dechlorination, samplepreservation, pH adjustment, etc.

Unconcentrated samples include such water samples which are not dilutedor concentrated such that they may be directly injected from the source,with or without minimal processing, into the system for analysis. Theterm “minimal processing” includes the addition of preservatives,buffers, etc. in order to modulate sample stability, pH, etc.

In various embodiments, concentrated samples are analyzed for detectionand quantitation of PFAS analyte(s) at extremely low levels. As usedherein, “concentrated samples” include samples obtained via one or moreof the following steps: i) the extraction of PFAS analyte(s) from afirst volume of water (typically an aqueous sample obtained directlyfrom a water source) into second volume of a water-immiscible solvent,wherein the second volume of a water-immiscible solvent is less than orsubstantially the same; ii) partial or complete evaporation of thewater-immiscible solvent to concentrate the PFAS analyte(s) containedtherein; and iii) re-dissolving the PFAS analyte(s) into a third volumeof water with or without the concomitant introduction of preservatives,buffers, and/or dechlorination agents, wherein the third volume of wateris of a lesser volume than the first volume of water.

In some embodiments of the present invention, concentrated andunconcentrated samples of PFAS analyte(s) include samples collected andprepared from soil and plants, as described elsewhere (e.g., see Husetand Barry, “Quantitative determination of perfluoroalkyl substances(PFAS) in soil, water, and home garden produce”, MethodsX 5 (2018)697-704). In some embodiments, concentrated and unconcentrated samplesof PFAS analyte(s) include samples collected from urine and blood.

As used herein, the term “PFAS analyte solution,” “PFAS analyte(s) in asolution,” “a solution containing PFAS analyte(s),” and the like,includes a homogeneous solution of PFAS analyte(s), which includesconcentrated and unconcentrated PFAS analyte samples as well asstandards, etc. As is well-known in the art, for any analyte to beinjected onto an LC/MS/MS system, it must be in a homogeneous solutionof a solvent suitable for injection onto an LC column.

It will be understood that within a known volume of an analyte solutionthat has a known concentration, the amount of analyte is also known andreadily calculated. For example, 75 microliters (∝L or ∝l) of a PFASanalyte solution that has a concentration of 0.010 micrograms per liter(0.010 ∝g/L or ∝g/l) contains 7.5×10⁻⁷ ∝g of the PFAS analyte accordingto the equation: (0.010 ∝g/L)×(75 ∝L)×(10⁻⁶ L/∝L)=7.5×10⁻⁷ ∝g. Thus, 75∝L of a 0.0020 ∝g/L PFAS analyte solution contains 1.5×10⁻⁷ ∝g of thePFAS analyte, 75 ∝L of a 0.25 ∝g/L PFAS analyte solution contains1.9×10⁻⁵ ∝g of the PFAS analyte and 75 ∝L of a 0.070 ∝g/L PFAS analytesolution contains 5.3×10⁻⁶ ∝g of the PFAS analyte.

Throughout this description and claims, it will be understood that anyknown volume of an analyte solution with a known concentration of saidanalyte may be expressed in terms of a known mass of said analyte.

Herein, analyte concentration may be expressed as parts per trillion(ppt) according to the relationship 1 ng/L=1 ppt. Thus, 0.010 μg/L maybe expressed as 10 ppt, 0.0020 μg/L may be expressed as 2 ppt, 0.070μg/L may be expressed as 70 ppt, and 0.25 μg/L may be expressed as 250ppt. Because the relationship between ppt and μg/L is defined above, itis now established that a known volume containing a known ppt of ananalyte may also be expressed in terms of a known mass of said analyte.

Embodiments of the present invention provide a method and system todetermine the concentration of a PFAS analyte of formula C_(n)F(2n+1)—Xin solutions such as unconcentrated samples within a range ofapproximately 0.0020 μg/L to approximately 0.25 μg/L based onapproximately a 75 μL injection volume using ESI conditions on anLC/MS/MS instrument as described infra. It will be readily apparent toone skilled in the art that, since the sensitivity of the method andsystem described herein is dependent on injection volume, injectionvolumes greater than approximately 75 μL will produce quantitation ofsolutions having a concentration of PFAS analyte of formulaC_(n)F(2n+1)—X in solutions that is lower than 0.0020 ∝g/L. In someembodiments, a concentration of a PFAS analyte of formulaC_(n)F_((2n+1))—X in solutions such as unconcentrated samples isdetermined within a range of approximately 0.0020 ∝g/L to approximately0.24 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.23 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.22 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.21 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.20 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.19 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.18 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.17 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.16 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.15 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.14 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.13 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.12 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.11 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.10 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.090 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.080 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.070 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.060 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.050 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.040 ∝g/L. In someembodiments, the range is approximately 0.0020 ∝g/L to approximately0.030 ∝g/L. In some embodiments, the range is approximately 0.0020 ∝g/Lto approximately 0.020 ∝g/L. In some embodiments, the range isapproximately 0.0020 ∝g/L to approximately 0.010 ∝g/L.

Embodiments of the present invention provide a method and system todetermine a concentration of a PFAS analyte of formula C_(n)F(2n+1)—X insolutions such as unconcentrated samples within a range of approximately0.010 μg/L to approximately 0.25 μg/L based on a 75 μL injection volumeusing ESI conditions on an LC/MS/MS instrument as described infra.

In some embodiments, a concentration of a PFAS analyte of formulaC_(n)F(2n+1)—X in solutions such as unconcentrated samples is determinedwithin a range of approximately 0.010 μg/L to approximately 0.24 μg/L.In some embodiments, the range is approximately 0.010 μg/L toapproximately 0.23 μg/L. In some embodiments, the range is approximately0.010 μg/L to approximately 0.22 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.21 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately 0.20μg/L. In some embodiments, the range is approximately 0.010 μg/L toapproximately 0.19 μg/L. In some embodiments, the range is approximately0.010 μg/L to approximately 0.18 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.17 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately 0.16μg/L. In some embodiments, the range is approximately 0.010 μg/L toapproximately 0.15 μg/L. In some embodiments, the range is approximately0.010 μg/L to approximately 0.14 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.13 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately 0.12μg/L. In some embodiments, the range is approximately 0.010 μg/L toapproximately 0.11 μg/L. In some embodiments, the range is approximately0.010 μg/L to approximately 0.10 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.090 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately0.080 μg/L. In some embodiments, the range is approximately 0.010 μg/Lto approximately 0.070 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.060 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately0.050 μg/L. In some embodiments, the range is approximately 0.010 μg/Lto approximately 0.040 μg/L. In some embodiments, the range isapproximately 0.010 μg/L to approximately 0.030 μg/L. In someembodiments, the range is approximately 0.010 μg/L to approximately0.020 μg/L.

Embodiments of the present invention provide a method and system todetermine a concentration of a PFAS analyte of formula C_(n)F(2n+1)—X insolutions such as unconcentrated samples within a range of approximately0.070 μg/L to approximately 0.25 μg/L based on a 75 μL injection volumeusing ESI conditions on an LC/MS/MS instrument as described infra.

In some embodiments, a concentration of a PFAS analyte of formulaC_(n)F(2n+1)—X in solutions such as unconcentrated samples is determinedwithin a range of approximately 0.070 μg/L to approximately 0.24 μg/L.In some embodiments, the range is approximately 0.070 μg/L toapproximately 0.23 μg/L. In some embodiments, the range is approximately0.070 μg/L to approximately 0.22 μg/L. In some embodiments, the range isapproximately 0.070 μg/L to approximately 0.21 μg/L. In someembodiments, the range is approximately 0.070 μg/L to approximately 0.20μg/L. In some embodiments, the range is approximately 0.070 μg/L toapproximately 0.19 μg/L. In some embodiments, the range is approximately0.070 μg/L to approximately 0.18 μg/L. In some embodiments, the range isapproximately 0.070 μg/L to approximately 0.17 μg/L. In someembodiments, the range is approximately 0.070 μg/L to approximately 0.16μg/L. In some embodiments, the range is approximately 0.070 μg/L toapproximately 0.15 μg/L. In some embodiments, the range is approximately0.070 μg/L to approximately 0.14 μg/L. In some embodiments, the range isapproximately 0.070 μg/L to approximately 0.13 μg/L. In someembodiments, the range is approximately 0.070 μg/L to approximately 0.12μg/L. In some embodiments, the range is approximately 0.070 μg/L toapproximately 0.11 μg/L. In some embodiments, the range is approximately0.070 μg/L to approximately 0.10 μg/L. In some embodiments, the range isapproximately 0.070 μg/L to approximately 0.090 μg/L. In someembodiments, the range is approximately 0.070 μg/L to approximately0.080 μg/L.

Embodiments of the present invention provide a method and system todetermine a concentration of a PFAS analyte of formula C_(n)F(2n+1)—X insolutions such as unconcentrated samples within a range of approximately2.0 ppt to approximately 250 ppt based on a 75 μL injection volume usingESI conditions on an LC/MS/MS instrument as described infra. Asexplained supra, wherein 1 ng/L=1 ppt (i.e. 1.0 μg/L=1.0×103 ppt), theembodiments described supra of determinable μg/L concentration ranges ofPFAS analytes apply when expressed as ppt.

It will be readily understood by a person having ordinary skill in theart that virtually any concentration of a PFAS analyte of formulaC_(n)F(2n+1)—X above 0.250 μg/L (250.0 ppt) within a solution isdeterminable by the method and system described herein via the use ofwell-known dilution techniques. In fact, such techniques are exemplifiedby the preparation of analyte standards as described infra.

Embodiments of the present invention provide a method and system todetermine an amount of a PFAS analyte of formula C_(n)F(2n+1)—X that isinjected from a solution such as unconcentrated sample onto an LC/MS/MSinstrument based on a known injected volume of determined concentration.The individual amount of a PFAS analyte that are determinable perinjection range from approximately 1.5×10-7 μg to approximately 1.9×10⁻⁵μg using ESI conditions as described infra.

In some embodiments, the amount of a PFAS analyte determinable perinjection is within a range of approximately 1.5×10-7 μg toapproximately 1.8×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 1.5×10-7 μg to approximately 1.7×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 1.5×10-7 μg to approximately 1.6×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately1.5×10-7 μg to approximately 1.5×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 1.5×10-7 μg toapproximately 1.4×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 1.5×10-7 μg to approximately 1.3×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 1.5×10-7 μg to approximately 1.2×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately1.5×10-7 μg to approximately 1.1×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 1.5×10-7 μg toapproximately 9.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 1.5×10-7 μg to approximately 9.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 1.5×10-7 μg to approximately 8.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately1.5×10-7 μg to approximately 7.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 1.5×10-7 μg toapproximately 6.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 1.5×10-7 μg to approximately 6.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 1.5×10-7 μg to approximately 5.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately1.5×10-7 μg to approximately 4.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 1.5×10-7 μg toapproximately 3.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 1.5×10-7 μg to approximately 3.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 1.5×10-7 μg to approximately 2.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately1.5×10-7 μg to approximately 1.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 1.5×10-7 μg toapproximately 7.5×10-7 μg.

Embodiments of the present invention provide a method and system todetermine an amount of a PFAS analyte of formula C_(n)F(2n+1)—X that isinjected from a solution such as unconcentrated sample onto an LC/MS/MSinstrument based on a known injected volume of determined concentration.The individual amount of a PFAS analyte that are determinable perinjection range from approximately 7.5×10-7 μg to approximately 1.9×10⁻⁵μg using ESI conditions as described infra.

In some embodiments, the amount of a PFAS analyte determinable perinjection is within a range of approximately 7.5×10-7 μg toapproximately 1.8×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 7.5×10-7 μg to approximately 1.7×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 7.5×10-7 μg to approximately 1.6×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately7.5×10-7 μg to approximately 1.5×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 7.5×10-7 μg toapproximately 1.4×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 7.5×10-7 μg to approximately 1.3×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 7.5×10-7 μg to approximately 1.2×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately7.5×10-7 μg to approximately 1.1×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 7.5×10-7 μg toapproximately 9.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 7.5×10-7 μg to approximately 9.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 7.5×10-7 μg to approximately 8.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately7.5×10-7 μg to approximately 7.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 7.5×10-7 μg toapproximately 6.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 7.5×10-7 μg to approximately 6.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 7.5×10-7 μg to approximately 5.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately7.5×10-7 μg to approximately 4.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 7.5×10-7 μg toapproximately 3.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 7.5×10-7 μg to approximately 3.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 7.5×10-7 μg to approximately 2.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately7.5×10-7 μg to approximately 1.5×10-6 μg.

Embodiments of the present invention provide a method and system todetermine an amount of a PFAS analyte of formula C_(n)F(2n+1)—X that isinjected from a solution such as unconcentrated sample onto an LC/MS/MSinstrument based on a known injected volume of determined concentration.The individual amount of a PFAS analyte that are determinable perinjection range from approximately 5.3×10-6 μg to approximately 1.9×10⁻⁵μg using ESI conditions as described infra.

In some embodiments, the amount of a PFAS analyte determinable perinjection is within a range of approximately 5.3×10-6 μg toapproximately 1.8×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 5.3×10-6 μg to approximately 1.7×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 5.3×10-6 μg to approximately 1.6×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately5.3×10-6 μg to approximately 1.5×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 5.3×10-6 μg toapproximately 1.4×10⁻⁵ μg. In some embodiments, the determinable amountis within a range of approximately 5.3×10-6 μg to approximately 1.3×10⁻⁵μg. In some embodiments, the determinable amount is within a range ofapproximately 5.3×10-6 μg to approximately 1.2×10⁻⁵ μg. In someembodiments, the determinable amount is within a range of approximately5.3×10-6 μg to approximately 1.1×10⁻⁵ μg. In some embodiments, thedeterminable amount is within a range of approximately 5.3×10-6 μg toapproximately 9.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 5.3×10-6 μg to approximately 9.0×10-6μg. In some embodiments, the determinable amount is within a range ofapproximately 5.3×10-6 μg to approximately 8.3×10-6 μg. In someembodiments, the determinable amount is within a range of approximately5.3×10-6 μg to approximately 7.5×10-6 μg. In some embodiments, thedeterminable amount is within a range of approximately 5.3×10-6 μg toapproximately 6.8×10-6 μg. In some embodiments, the determinable amountis within a range of approximately 5.3×10-6 μg to approximately 6.0×10-6μg.

Embodiments of the present invention utilize ESI on an LC/MS/MS systemto determine PFAS analyte concentration and amount. ESI is an ionizationtechnique used in mass spectrometry to produce ions using anelectrospray in which a high voltage is applied to a liquid to create anaerosol that is ionized.

FIG. 1 depicts a block diagram of components 100 of an LC/MS/MS systemused to determine a concentration and/or amount of a PFAS analyte insamples in accordance with an exemplary embodiment of the presentinvention. It should be appreciated that FIG. 1 provides only anillustration of one implementation and does not imply any limitationswith regard to other systems in which embodiments of the presentinvention may be implemented. Other modifications to the depicted systemmay be made without departing from the scope of the present invention.

LC/MS/MS system 100 includes injector 110, LC column 115, ESI ionizercomponent 120, triple quadrupole mass spectrometer (TQMS) component 125,ion detector 130, and mass spectrum read-out software 135.

TQMS 125 includes two quadrupole mass analyzers in series (125Q1 and125Q3) with a non-mass-resolving quadrupole (125Q2) between them to actas a cell for collision-induced dissociation. All three quadrupole massanalyzers consist of four cylindrical rods (for reasons of simplicitythey are schematically represented by the labeled parallel bars in FIG.1). The four cylindrical bars are set parallel to each other. For 125Q1and 125Q3, each opposing rod pair is connected together electrically anda radio frequency (RF) voltage with a DC offset voltage is appliedbetween one pair of rods and the other. Ions travel down the quadrupolebetween the rods. Only ions of a certain mass-to-charge ratio will reachdetector 130 for a given ratio of voltages. Other ions have unstabletrajectories and will collide with the rods. This permits selection ofan ion with a particular m/z or allows the operator to scan for a rangeof m/z-values by continuously varying the applied voltage. Quadrapole125Q2 is an RF-only quadrupole (non-mass filtering) for collisioninduced dissociation of selected parent ion(s) from 125Q1. Subsequentfragments are passed through to 125Q3 where they may be filtered orfully scanned.

In an embodiment, an aliquot of PFAS analyte sample 105 is injected intoinjector 110 and the injection liquid 101 is resolved into various PFASanalytes by LC column 115 using, for example, the column, conditions,and gradient example shown and described for Table 6.

After eluting through LC column 115, the PFAS analyte-containing eluent102 is subjected to ESI 120. Conditions for ionization of PFAS analytesusing ESI techniques as depicted by ESI 120 will be detailed anddescribed infra in embodiments of the present invention.

After ionization of the PFAS-containing eluent by ESI 120, the ion(s)103 are passed through the first quadrupole mass analyzer, 125Q1, whichserves as a filter for selecting desired PFAS analyte ions 104. Thesecond quadrupole mass analyzer, 125Q2, allows for collision of selectedions 104 to produce one or more children ions 106 that then pass throughthe third quadrupole mass analyzer, 125Q3. Quadrupole mass analyzer125Q3 provides a scan of the entire m/z range of the product ion(s) 106,providing output 107 for fragments 106. Quantification of selected ion104 can then be deduced from the ion fragmentation output 107 receivedby ion detector 130 and processed by mass spectrum read-out software135.

Embodiments of the present invention employ ESI settings on an LC/MS/MSsystem such as the system described above that include: i) an ionpolarity setting to cause the formation of negative or positive ions;ii) a probe gas temperature setting for controlling the temperature ofan inert drying gas (typically nitrogen) that is used to promote theremoval of solvent from aerosol particles in spray ionization; iii) agas flow setting for controlling the volume per unit time that thedrying gas is dispersed; iv) a nebulizer setting for controlling thepressure utilized for the mass spectrometer nebulizer, which delivers afine mist using the specified pressure; v) a sheath gas heater settingfor controlling a temperature setting for heating a sheath gas, which isan inert gas (typically nitrogen) introduced through a tube that iscoaxial with the electrospray emitter to pneumatically assist theformation of the sprayed droplets; vi) a sheath gas flow setting forcontrolling a volume per unit time that the sheath gas is dispersed;vii) a capillary voltage setting for controlling a voltage applied tothe tip of a metal capillary relative to the surrounding source-samplingcone or heated capillary, which creates a strong electric field causesthe dispersion of the sample solution into an aerosol of highly chargedelectrospray droplets; and viii) a V charging setting for controlling acharging electrode within the instrument.

A non-limiting example of ESI settings used on an AGILENT 6495 massspectrometer for analyzing concentrations and amounts of PFAS analytesin solutions such as unconcentrated samples is shown in Table 2 below.

TABLE 2 Example of ESI settings used in an embodiment of the presentinvention. Polarity Negative ion ESI Conditions Gas Temp (° C.) 120 GasFlow (1/min) 11 Nebulizer (psi) 20 Sheath Gas Heater 400 Sheath Gas Flow8 Capillary (V) 1500 V Charging 0 Ion Funnel Parameters High Pressure RF110 Low Pressure RF 80

For Table 2 above, the “Ion Funnel Parameters” refers to settings for anion funnel, which is used to focus a beam of ions using a series ofstacked ring electrodes with decreasing inner diameter. A combined radiofrequency (RF) and fixed electrical potential is applied to the grids.

In various embodiments of the present invention, concentrations andamounts of PFAS analytes in solutions such as unconcentrated samples areanalyzed using ESI conditions include a probe gas temperature setting(“Gas Temp (° C.)”) of approximately 120° C. to approximately 180° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 175° C. In some embodiments, the probe gastemperature setting is approximately 120° C. to approximately 170° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 165° C. In some embodiments, the probe gastemperature setting is approximately 120° C. to approximately 160° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 155° C. In some embodiments, the probe gastemperature setting is approximately 120° C. to approximately 150° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 145° C. In some embodiments, the probe gastemperature setting is approximately 120° C. to approximately 140° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 135° C. In some embodiments, the probe gastemperature setting is approximately 120° C. to approximately 130° C. Insome embodiments, the probe gas temperature setting is approximately120° C. to approximately 125° C. In some embodiments, the probe gastemperature setting is approximately 120° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 125° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 125° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 125° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 125° C.to approximately 165° C. In some embodiments, ESI conditions include aprobe probe gas temperature setting of approximately 125° C. toapproximately 160° C. In some embodiments, the probe gas temperaturesetting is approximately 125° C. to approximately 155° C. In someembodiments, the probe gas temperature setting is approximately 125° C.to approximately 150° C. In some embodiments, the probe gas temperaturesetting is approximately 125° C. to approximately 145° C. In someembodiments, the probe gas temperature setting is approximately 125° C.to approximately 140° C. In some embodiments, the probe gas temperaturesetting is approximately 125° C. to approximately 135° C. In someembodiments, the probe gas temperature setting is approximately 125° C.to approximately 130° C. In some embodiments, the probe gas temperaturesetting is approximately 125° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 130° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 130° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 130° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 130° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 130° C. to approximately 160° C. In someembodiments, the probe gas temperature setting is approximately 130° C.to approximately 155° C. In some embodiments, the probe gas temperaturesetting is approximately 130° C. to approximately 150° C. In someembodiments, the probe gas temperature setting is approximately 130° C.to approximately 145° C. In some embodiments, the probe gas temperaturesetting is approximately 130° C. to approximately 140° C. In someembodiments, the probe gas temperature setting is approximately 130° C.to approximately 135° C. In some embodiments, the probe gas temperaturesetting is approximately 130° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 135° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 135° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 135° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 135° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 135° C. to approximately 160° C. In someembodiments, the probe gas temperature setting is approximately 135° C.to approximately 155° C. In some embodiments, the probe gas temperaturesetting is approximately 135° C. to approximately 150° C. In someembodiments, the probe gas temperature setting is approximately 135° C.to approximately 145° C. In some embodiments, the probe gas temperaturesetting is approximately 135° C. to approximately 140° C. In someembodiments, the probe gas temperature setting is approximately 135° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 140° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 140° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 140° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 140° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 140° C. to approximately 160° C. In someembodiments, the probe gas temperature setting is approximately 140° C.to approximately 155° C. In some embodiments, the probe gas temperaturesetting is approximately 140° C. to approximately 150° C. In someembodiments, the probe gas temperature setting is approximately 140° C.to approximately 145° C. In some embodiments, the probe gas temperaturesetting is approximately 140° C.

In some embodiments, the probe gas temperature setting is approximately145° C. to approximately 180° C. In some embodiments, the probe gastemperature setting is approximately 145° C. to approximately 175° C. Insome embodiments, the probe gas temperature setting is approximately145° C. to approximately 170° C. In some embodiments, the probe gastemperature setting is approximately 145° C. to approximately 165° C. Insome embodiments, the probe gas temperature setting is approximately145° C. to approximately 160° C. In some embodiments, the probe gastemperature setting is approximately 145° C. to approximately 155° C. Insome embodiments, the probe gas temperature setting is approximately145° C. to approximately 150° C. In some embodiments, the probe gastemperature setting is approximately 145° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 150° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 150° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 150° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 150° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 150° C. to approximately 160° C. In someembodiments, the probe gas temperature setting is approximately 150° C.to approximately 155° C. In some embodiments, the probe gas temperaturesetting is approximately 150° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 155° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 155° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 155° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 155° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 155° C. to approximately 160° C. In someembodiments, the probe gas temperature setting is approximately 155° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 160° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 160° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 160° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 160° C.to approximately 165° C. In some embodiments, the probe gas temperaturesetting is approximately 160° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 165° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 165° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 165° C. to approximately 170° C. In someembodiments, the probe gas temperature setting is approximately 165° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 170° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 170° C.to approximately 175° C. In some embodiments, the probe gas temperaturesetting is approximately 170° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 175° C. to approximately 180° C. In someembodiments, the probe gas temperature setting is approximately 175° C.

In some embodiments, ESI conditions include a probe gas temperaturesetting of approximately 180° C.

In some embodiments when the PFAS analyte solution includes PFBA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFBA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFBS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFBS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFHpA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFHpA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFHxA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFHxA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFHxS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFHxS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFPeS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 180° C. In some embodiments when the PFASanalyte solution includes PFPeS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFDA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 160° C. In some embodiments when the PFASanalyte solution includes PFDA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFHpS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 160° C. In some embodiments when the PFASanalyte solution includes PFHpS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFOS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 160° C. In some embodiments when the PFASanalyte solution includes PFOS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFNA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 140° C. In some embodiments when the PFASanalyte solution includes PFNA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFNS asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 160° C. In some embodiments when the PFASanalyte solution includes PFNS as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments when the PFAS analyte solution contains PFOA asanalyte, the probe gas temperature setting ranges from approximately120° C. to approximately 160° C. In some embodiments when the PFASanalyte solution includes PFOA as analyte, the probe gas temperaturesetting is approximately 120° C.

In some embodiments, the ESI probe gas temperature setting is set on anAGILENT 6490 or 6495 mass spectrometer. In exemplary embodiments, theESI gas temperature setting is set on an AGILENT 6495 mass spectrometer.

In various embodiments, ESI conditions include a sheath gas heatersetting (“Sheath Gas Heater”) of approximately 250° C. to approximately400° C. In some embodiments, the sheath gas heater setting isapproximately 250° C. to approximately 395° C. In some embodiments, thesheath gas heater setting is approximately 250° C. to approximately 390°C. In some embodiments, the sheath gas heater setting is approximately250° C. to approximately 385° C. In some embodiments, the sheath gasheater setting is approximately 250° C. to approximately 380° C. In someembodiments, the sheath gas heater setting is approximately 250° C. toapproximately 375° C. In some embodiments, the sheath gas heater settingis approximately 250° C. to approximately 370° C. In some embodiments,the sheath gas heater setting is approximately 250° C. to approximately365° C. In some embodiments, the sheath gas heater setting isapproximately 250° C. to approximately 360° C. In some embodiments, thesheath gas heater setting is approximately 250° C. to approximately 355°C. In some embodiments, the sheath gas heater setting is approximately250° C. to approximately 350° C. In some embodiments, the sheath gasheater setting is approximately 250° C. to approximately 345° C. In someembodiments, the sheath gas heater setting is approximately 250° C. toapproximately 340° C. In some embodiments, the sheath gas heater settingis approximately 250° C. to approximately 335° C. In some embodiments,the sheath gas heater setting is approximately 250° C. to approximately330° C. In some embodiments, the sheath gas heater setting isapproximately 250° C. to approximately 325° C. In some embodiments, thesheath gas heater setting is approximately 250° C. to approximately 320°C. In some embodiments, the sheath gas heater setting is approximately250° C. to approximately 315° C. In some embodiments, the sheath gasheater setting is approximately 250° C. to approximately 310° C. In someembodiments, the sheath gas heater setting is approximately 250° C. toapproximately 305° C. In some embodiments, the sheath gas heater settingis approximately 250° C. to approximately 300° C. In some embodiments,the sheath gas heater setting is approximately 250° C. to approximately295° C. In some embodiments, the sheath gas heater setting isapproximately 250° C. to approximately 290° C. In some embodiments, thesheath gas heater setting is approximately 250° C. to approximately 285°C. In some embodiments, the sheath gas heater setting is approximately250° C. to approximately 280° C. In some embodiments, the sheath gasheater setting is approximately 250° C. to approximately 275° C. In someembodiments, the sheath gas heater setting is approximately 250° C. toapproximately 270° C. In some embodiments, the sheath gas heater settingis approximately 250° C. to approximately 265° C. In some embodiments,the sheath gas heater setting is approximately 250° C. to approximately260° C. In some embodiments, the sheath gas heater setting isapproximately 250° C. to approximately 255° C. In some embodiments, thesheath gas heater setting is approximately 250° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 255° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 255° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 255° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 255° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 255° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 255° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately255° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 255° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 255° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 255° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 255° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 255° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 255° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately255° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 255° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 255° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 255° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 255° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 255° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 255° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately255° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 255° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 255° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 255° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 255° C. to approximately280° C. In some embodiments, the sheath gas heater setting isapproximately 255° C. to approximately 275° C. In some embodiments, thesheath gas heater setting is approximately 255° C. to approximately 270°C. In some embodiments, the sheath gas heater setting is approximately255° C. to approximately 265° C. In some embodiments, the sheath gasheater setting is approximately 255° C. to approximately 260° C. In someembodiments, the sheath gas heater setting is approximately 255° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 260° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 260° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 260° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 260° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 260° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 260° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately260° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 260° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 260° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 260° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 260° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 260° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 260° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately260° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 260° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 260° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 260° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 260° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 260° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 260° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately260° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 260° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 260° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 260° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 260° C. to approximately280° C. In some embodiments, the sheath gas heater setting isapproximately 260° C. to approximately 275° C. In some embodiments, thesheath gas heater setting is approximately 260° C. to approximately 270°C. In some embodiments, the sheath gas heater setting is approximately260° C. to approximately 265° C. In some embodiments, the sheath gasheater setting is approximately 260° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 265° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 265° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 265° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 265° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 265° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 265° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately265° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 265° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 265° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 265° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 265° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 265° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 265° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately265° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 265° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 265° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 265° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 265° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 265° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 265° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately265° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 265° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 265° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 265° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 265° C. to approximately280° C. In some embodiments, the sheath gas heater setting isapproximately 265° C. to approximately 275° C. In some embodiments, thesheath gas heater setting is approximately 265° C. to approximately 270°C. In some embodiments, the sheath gas heater setting is approximately265° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 270° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 270° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 270° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 270° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 270° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 270° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately270° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 270° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 270° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 270° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 270° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 270° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 270° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately270° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 270° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 270° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 270° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 270° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 270° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 270° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately270° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 270° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 270° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 270° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 270° C. to approximately280° C. In some embodiments, the sheath gas heater setting isapproximately 270° C. to approximately 275° C. In some embodiments, thesheath gas heater setting is approximately 270° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 275° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 275° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 275° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 275° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 275° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 275° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately275° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 275° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 275° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 275° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 275° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 275° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 275° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately275° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 275° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 275° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 275° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 275° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 275° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 275° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately275° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 275° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 275° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 275° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 275° C. to approximately280° C. In some embodiments, the sheath gas heater setting isapproximately 275° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 280° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 280° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 280° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 280° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 280° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 280° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately280° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 280° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 280° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 280° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 280° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 280° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 280° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately280° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 280° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 280° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 280° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 280° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 280° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 280° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately280° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 280° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 280° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 280° C. to approximately 285° C. In some embodiments,the sheath gas heater setting is approximately 280° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 285° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 285° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 285° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 285° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 285° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 285° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately285° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 285° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 285° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 285° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 285° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 285° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 285° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately285° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 285° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 285° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 285° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 285° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 285° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 285° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately285° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 285° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 285° C. toapproximately 290° C. In some embodiments, the sheath gas heater settingis approximately 285° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 290° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 290° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 290° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 290° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 290° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 290° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately290° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 290° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 290° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 290° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 290° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 290° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 290° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately290° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 290° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 290° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 290° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 290° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 290° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 290° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately290° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 290° C. to approximately 295° C. In someembodiments, the sheath gas heater setting is approximately 290° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 295° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 295° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 295° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 295° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 295° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 295° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately295° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 295° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 295° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 295° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 295° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 295° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 295° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately295° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 295° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 295° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 295° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 295° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 295° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 295° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately295° C. to approximately 300° C. In some embodiments, the sheath gasheater setting is approximately 295° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 300° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 300° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 300° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 300° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 300° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 300° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately300° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 300° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 300° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 300° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 300° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 300° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 300° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately300° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 300° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 300° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 300° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 300° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 300° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 300° C. to approximately 305°C. In some embodiments, the sheath gas heater setting is approximately300° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 305° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 305° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 305° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 305° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 305° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 305° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately305° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 305° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 305° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 305° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 305° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 305° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 305° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately305° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 305° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 305° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 305° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 305° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 305° C. to approximately 310° C. In some embodiments, thesheath gas heater setting is approximately 305° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 310° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 310° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 310° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 310° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 310° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 310° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately310° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 310° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 310° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 310° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 310° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 310° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 310° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately310° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 310° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 310° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 310° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 310° C. to approximately315° C. In some embodiments, the sheath gas heater setting isapproximately 310° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 315° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 315° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 315° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 315° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 315° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 315° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately315° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 315° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 315° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 315° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 315° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 315° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 315° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately315° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 315° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 315° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 315° C. to approximately 320° C. In some embodiments,the sheath gas heater setting is approximately 315° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 320° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 320° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 320° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 320° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 320° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 320° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately320° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 320° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 320° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 320° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 320° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 320° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 320° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately320° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 320° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 320° C. toapproximately 325° C. In some embodiments, the sheath gas heater settingis approximately 320° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 325° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 325° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 325° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 325° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 325° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 325° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately325° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 325° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 325° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 325° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 325° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 325° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 325° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately325° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 325° C. to approximately 330° C. In someembodiments, the sheath gas heater setting is approximately 325° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 330° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 330° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 330° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 330° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 330° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 330° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately330° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 330° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 330° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 330° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 330° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 330° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 330° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately330° C. to approximately 335° C. In some embodiments, the sheath gasheater setting is approximately 330° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 335° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 335° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 335° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 335° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 335° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 335° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately335° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 335° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 335° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 335° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 335° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 335° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 335° C. to approximately 340°C. In some embodiments, the sheath gas heater setting is approximately335° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 340° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 340° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 340° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 340° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 340° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 340° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately340° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 340° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 340° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 340° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 340° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 340° C. to approximately 345° C. In some embodiments, thesheath gas heater setting is approximately 340° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 345° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 345° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 345° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 345° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 345° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 345° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately345° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 345° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 345° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 345° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 345° C. to approximately350° C. In some embodiments, the sheath gas heater setting isapproximately 345° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 350° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 350° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 350° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 350° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 350° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 350° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately350° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 350° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 350° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 350° C. to approximately 355° C. In some embodiments,the sheath gas heater setting is approximately 350° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 355° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 355° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 355° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 355° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 355° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 355° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately355° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 355° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 355° C. toapproximately 360° C. In some embodiments, the sheath gas heater settingis approximately 355° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 360° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 360° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 360° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 360° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 360° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 360° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately360° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 360° C. to approximately 365° C. In someembodiments, the sheath gas heater setting is approximately 360° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 365° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 365° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 365° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 365° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 365° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 365° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately365° C. to approximately 370° C. In some embodiments, the sheath gasheater setting is approximately 365° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 370° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 370° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 370° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 370° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 370° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 370° C. to approximately 375°C. In some embodiments, the sheath gas heater setting is approximately370° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 375° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 375° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 375° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 375° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 375° C. to approximately 380° C. In some embodiments, thesheath gas heater setting is approximately 375° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 380° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 380° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 380° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 380° C. to approximately385° C. In some embodiments, the sheath gas heater setting isapproximately 380° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 385° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 385° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 385° C. to approximately 390° C. In some embodiments,the sheath gas heater setting is approximately 385° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 390° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 390° C. toapproximately 395° C. In some embodiments, the sheath gas heater settingis approximately 390° C.

In various embodiments, ESI conditions include a sheath gas heatersetting of approximately 395° C. to approximately 400° C. In someembodiments, the sheath gas heater setting is approximately 395° C. Insome embodiments, the sheath gas heater setting is approximately 400° C.

In some embodiments when the PFAS analyte solution includes PFBA asanalyte, the sheath gas heater setting ranges from approximately 250° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFBA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFBS asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFBS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFHpA asanalyte, the sheath gas heater setting ranges from approximately 275° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFHpA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFHxA asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFHxA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFHxS asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFHxS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFPeS asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFPeS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFDA asanalyte, the sheath gas heater setting ranges from approximately 275° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFDA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFHpS asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFHpS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFOS asanalyte, the sheath gas heater setting ranges from approximately 350° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFOS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFNA asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFNA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFNS asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFNS as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments when the PFAS analyte solution contains PFOA asanalyte, the sheath gas heater setting ranges from approximately 300° C.to approximately 400° C. In some embodiments when the PFAS analytesolution includes PFOA as analyte, the sheath gas heater setting isapproximately 400° C.

In some embodiments, the ESI sheath gas heater setting is set on anAGILENT 6490 or 6495 mass spectrometer. In exemplary embodiments, theESI sheath gas heater setting is set on an AGILENT 6495 massspectrometer.

In various embodiments, ESI conditions include a sheath gas flow(“Sheath Gas Flow”) of approximately 8 L/min to approximately 12 L/min.In some embodiments, the sheath gas flow is approximately 8 L/min toapproximately 11 L/min. In some embodiments, the sheath gas flow isapproximately 8 L/min to approximately 10 L/min. In some embodiments,the sheath gas flow is approximately 8 L/min to approximately 9 L/min.In some embodiments, the sheath gas flow is approximately 8 L/min.

In various embodiments, ESI conditions include a sheath gas flow ofapproximately 9 L/min to approximately 12 L/min. In some embodiments,the sheath gas flow is approximately 9 L/min to approximately 11 L/min.In some embodiments, the sheath gas flow is approximately 9 L/min toapproximately 10 L/min. In some embodiments, the sheath gas flow isapproximately 9 L/min.

In various embodiments, ESI conditions include a sheath gas flow ofapproximately 10 L/min to approximately 12 L/min. In some embodiments,the sheath gas flow is approximately 10 L/min to approximately 11 L/min.In some embodiments, the sheath gas flow is approximately 10 L/min.

In various embodiments, ESI conditions include a sheath gas flow ofapproximately 11 L/min to approximately 12 L/min. In some embodiments,the sheath gas flow is approximately 11 L/min. In some embodiments, thesheath gas flow is approximately 12 L/min.

In some embodiments when the PFAS analyte solution includes PFBA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution includes PFBA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFBS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution contains PFBS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFHpA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 10 L/min. In some embodiments when the PFAS analytesolution contains PFHpA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFHxA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 10 L/min. In some embodiments when the PFAS analytesolution contains PFHxA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFHxS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution contains PFHxS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFPeS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution contains PFPeS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFDA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 9 L/min. In some embodiments when the PFAS analytesolution contains PFDA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFHpS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution contains PFHpS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFOS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 9 L/min. In some embodiments when the PFAS analytesolution contains PFOS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFNA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 9 L/min. In some embodiments when the PFAS analytesolution contains PFNA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFNS asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 12 L/min. In some embodiments when the PFAS analytesolution contains PFNS as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments when the PFAS analyte solution contains PFOA asanalyte, the sheath gas flow setting ranges from approximately 8 L/minto approximately 10 L/min. In some embodiments when the PFAS analytesolution contains PFOA as analyte, the sheath gas flow setting isapproximately 8 L/min.

In some embodiments, the ESI sheath gas flow setting is set on anAGILENT 6490 or 6495 mass spectrometer. In exemplary embodiments, theESI sheath gas flow setting is set on an AGILENT 6495 mass spectrometer.

In various embodiments of the present invention, concentrations andamounts of PFAS analytes in solutions such as unconcentrated samples areanalyzed using ESI conditions that include a capillary voltage setting(“Capillary (V)”) of approximately 1500 V to approximately 4500 V. Insome embodiments, the capillary voltage setting is approximately 1500 Vto approximately 4400 V. In some embodiments, the capillary voltagesetting is approximately 1500 V to approximately 4300 V. In someembodiments, the capillary voltage setting is approximately 1500 V toapproximately 4200 V. In some embodiments, the capillary voltage settingis approximately 1500 V to approximately 4100 V. In some embodiments,the capillary voltage setting is approximately 1500 V to approximately4000 V. In some embodiments, the capillary voltage setting isapproximately 1500 V to approximately 3900 V. In some embodiments, thecapillary voltage setting is approximately 1500 V to approximately 3800V. In some embodiments, the capillary voltage setting is approximately1500 V to approximately 3700 V. In some embodiments, the capillaryvoltage setting is approximately 1500 V to approximately 3600 V. In someembodiments, the capillary voltage setting is approximately 1500 V toapproximately 3500 V. In some embodiments, the capillary voltage settingis approximately 1500 V to approximately 3400 V. In some embodiments,the capillary voltage setting is approximately 1500 V to approximately3300 V. In some embodiments, the capillary voltage setting isapproximately 1500 V to approximately 3200 V. In some embodiments, thecapillary voltage setting is approximately 1500 V to approximately 3100V. In some embodiments, the capillary voltage setting is approximately1500 V to approximately 3000 V. In some embodiments, the capillaryvoltage setting is approximately 1500 V to approximately 2900 V. In someembodiments, the capillary voltage setting is approximately 1500 V toapproximately 2800 V. In some embodiments, the capillary voltage settingis approximately 1500 V to approximately 2700 V. In some embodiments,the capillary voltage setting is approximately 1500 V to approximately2600 V. In some embodiments, the capillary voltage setting isapproximately 1500 V to approximately 2500 V. In some embodiments, thecapillary voltage setting is approximately 1500 V to approximately 2400V. In some embodiments, the capillary voltage setting is approximately1500 V to approximately 2300 V. In some embodiments, the capillaryvoltage setting is approximately 1500 V to approximately 2200 V. In someembodiments, the capillary voltage setting is approximately 1500 V toapproximately 2100 V. In some embodiments, the capillary voltage settingis approximately 1500 V to approximately 2000 V. In some embodiments,the capillary voltage setting is approximately 1500 V to approximately1900 V. In some embodiments, the capillary voltage setting isapproximately 1500 V to approximately 1800 V. In some embodiments, thecapillary voltage setting is approximately 1500 V to approximately 1700V. In some embodiments, the capillary voltage setting is approximately1500 V to approximately 1600 V. In some embodiments, the capillaryvoltage setting is approximately 1500 V.

In various embodiments of the present invention, concentrations andamounts of PFAS analytes in solutions such as unconcentrated samples areanalyzed using ESI conditions include a capillary voltage setting ofapproximately 4500 V. In some embodiments, the capillary voltage settingis approximately 4400 V. In some embodiments, the capillary voltagesetting is approximately 4300 V. In some embodiments, the capillaryvoltage setting is approximately 4200 V. In some embodiments, thecapillary voltage setting is approximately 4100 V. In some embodiments,the capillary voltage setting is approximately 4000 V. In someembodiments, the capillary voltage setting is approximately 3900 V. Insome embodiments, the capillary voltage setting is approximately 3800 V.In some embodiments, the capillary voltage setting is approximately 3700V. In some embodiments, the capillary voltage setting is approximately3600 V. In some embodiments, the capillary voltage setting isapproximately 3500 V. In some embodiments, the capillary voltage settingis approximately 3400 V. In some embodiments, the capillary voltagesetting is approximately 3300 V. In some embodiments, the capillaryvoltage setting is approximately 3200 V. In some embodiments, thecapillary voltage setting is approximately 3100 V. In some embodiments,the capillary voltage setting is approximately 3000 V. In someembodiments, the capillary voltage setting is approximately 2900 V. Insome embodiments, the capillary voltage setting is approximately 2800 V.In some embodiments, the capillary voltage setting is approximately 2700V. In some embodiments, the capillary voltage setting is approximately2600 V. In some embodiments, the capillary voltage setting isapproximately 2500 V. In some embodiments, the capillary voltage settingis approximately 2400 V. In some embodiments, the capillary voltagesetting is approximately 2300 V. In some embodiments, the capillaryvoltage setting is approximately 2200 V. In some embodiments, thecapillary voltage setting is approximately 2100 V. In some embodiments,the capillary voltage setting is approximately 2000 V. In someembodiments, the capillary voltage setting is approximately 1900 V. Insome embodiments, the capillary voltage setting is approximately 1800 V.In some embodiments, the capillary voltage setting is approximately 1700V. In some embodiments, the capillary voltage setting is approximately1600 V.

In some embodiments when the PFAS analyte solution includes PFBA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 2000 V. In some embodiments when the PFAS analytesolution includes PFBA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFBS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 2500 V. In some embodiments when the PFAS analytesolution includes PFBS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFHpA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 3000 V. In some embodiments when the PFAS analytesolution includes PFHpA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFHxA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 3000 V. In some embodiments when the PFAS analytesolution includes PFHxA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFHxS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 3000 V. In some embodiments when the PFAS analytesolution includes PFHxS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFPeS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 2500 V. In some embodiments when the PFAS analytesolution includes PFPeS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFDA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 4500 V. In some embodiments when the PFAS analytesolution includes PFDA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFHpS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 3000 V. In some embodiments when the PFAS analytesolution includes PFHpS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFOS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 2500 V. In some embodiments when the PFAS analytesolution includes PFOS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFNA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 4000 V. In some embodiments when the PFAS analytesolution includes PFNA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFNS asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 4000 V. In some embodiments when the PFAS analytesolution includes PFNS as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments when the PFAS analyte solution includes PFOA asanalyte, the capillary voltage setting ranges from approximately 1500 Vto approximately 3000 V. In some embodiments when the PFAS analytesolution includes PFOA as analyte, the capillary voltage setting isapproximately 1500 V.

In some embodiments, the ESI capillary voltage setting is set on anAGILENT 6490 or 6495 mass spectrometer. In exemplary embodiments, theESI capillary voltage setting is set on an AGILENT 6495 massspectrometer.

In various embodiments, ESI conditions include a gas flow setting (“GasFlow (1/min)”) of approximately 11 L/min to approximately 20 L/min. Insome embodiments, the gas flow setting is approximately 11 L/min toapproximately 19 L/min. In some embodiments, the gas flow setting isapproximately 11 L/min to approximately 18 L/min. In some embodiments,the gas flow setting is approximately 11 L/min to approximately 17L/min. In some embodiments, the gas flow setting is approximately 11L/min to approximately 16 L/min. In some embodiments, the gas flowsetting is approximately 11 L/min to approximately 15 L/min. In someembodiments, the gas flow setting is approximately 11 L/min toapproximately 14 L/min. In some embodiments, the gas flow setting isapproximately 11 L/min to approximately 13 L/min. In some embodiments,the gas flow setting is approximately 11 L/min to approximately 12L/min. In some embodiments, the gas flow setting is approximately 11L/min.

In various embodiments, ESI conditions include a gas flow setting ofapproximately 20 L/min. In some embodiments, the gas flow setting isapproximately 19 L/min. In some embodiments, the gas flow setting isapproximately 18 L/min. In some embodiments, the gas flow setting isapproximately 17 L/min. In some embodiments, the gas flow setting isapproximately 16 L/min. In some embodiments, the gas flow setting isapproximately 15 L/min. In some embodiments, the gas flow setting isapproximately 14 L/min. In some embodiments, the gas flow setting isapproximately 13 L/min. In some embodiments, the gas flow setting isapproximately 12 L/min.

In some embodiments when the PFAS analyte solution includes PFBA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFBA as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFBS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFBS as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFHpA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFHpA as analyte, the gas flow setting isapproximately 11 L/min.

In some embodiments when the PFAS analyte solution contains PFHxA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFHxA as analyte, the gas flow setting isapproximately 11 L/min.

In some embodiments when the PFAS analyte solution contains PFHxS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFHxS as analyte, the gas flow setting isapproximately 11 L/min.

In some embodiments when the PFAS analyte solution contains PFPeS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFPeS as analyte, the gas flow setting isapproximately 11 L/min.

In some embodiments when the PFAS analyte solution contains PFDA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFDA as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFHpS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFHpS as analyte, the gas flow setting isapproximately 11 L/min.

In some embodiments when the PFAS analyte solution contains PFOS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 12 L/min. In some embodiments when the PFAS analytesolution includes PFOS as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFNA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFNA as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFNS asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFNS as analyte, the gas flow setting is approximately11 L/min.

In some embodiments when the PFAS analyte solution contains PFOA asanalyte, the gas flow setting ranges from approximately 11 L/min toapproximately 20 L/min. In some embodiments when the PFAS analytesolution includes PFOA as analyte, the gas flow setting is approximately11 L/min.

In some embodiments, the ESI gas flow setting is set on an AGILENT 6490or 6495 mass spectrometer. In exemplary embodiments, the ESI gas flowsetting is set on an AGILENT 6495 mass spectrometer.

An example of minimum detection levels (MDL), minimum reporting levels(RL or MRL), and reporting ranges for the ESI settings shown above isshown in Table 3.

TABLE 3 Minimum Detection Levels (MDL), Minimum Reporting Levels (RL orMRL), and Reporting Ranges for an Exemplary Embodiment of the PresentInvention. MDL RL (MRL) Reporting Range Acronym [μg/L] [μg/L] [μg/L]PFBA 0.0025 0.010 0.010-0.25 PFBS 0.0041 0.010 0.010-0.25 PFDA 0.00440.010 0.010-0.25 PFHpA 0.0055 0.010 0.010-0.25 PFHpS 0.0087 0.0100.010-0.25 PFHxA 0.0017 0.010 0.010-0.25 PFHxS 0.0057 0.010 0.010-0.25PFNA 0.0052 0.010 0.010-0.25 PFPeS 0.0045 0.010 0.010-0.25 PFOA 0.000770.0020 0.0020-0.25  PFOS 0.00095 0.0020 0.0020-0.25 

MDLs (Method Detection Limits) are statistical values used to determineRLs/MRLs as described infra.

RLs/MRLs (Reporting Limits or Minimum Reporting Levels) are practicaland routinely achievable values of analyte concentration given ESIparameters such as described supra. The determination of RLs/MRLs isdescribed infra.

FIG. 2 illustrates processes, generally designated 200, for validating amethod to determine concentrations and amounts of PFAS analytes inunconcentrated samples and consequently determining concentrations andamounts of PFAS analytes in unconcentrated samples, in accordance withan exemplary embodiment of the present invention.

In step 205, working standards of PFAS analytes are prepared. Workingstandards include standards to calibrate and verify the calibration ofthe LC/MS/MS system both initially and ongoing (described in more detailinfra) as well as quality control standards analyzed in an analyticalrun such as laboratory fortified blanks, laboratory fortified matrixstandards, laboratory fortified matrix duplicates, etc. Laboratoryfortified blanks are an aliquot of preserved reagent water to whichknown quantities of the method analytes are added in the laboratory.Laboratory fortified blanks are analyzed like samples. The laboratoryfortified blanks are used to determine whether a method can makeaccurate and precise measurements. Laboratory fortified matrix standardsare aliquots of environmental samples to which known quantities of themethod analytes are added in the laboratory. Laboratory fortified matrixstandards are analyzed like samples. The laboratory fortified matrixstandards are used to determine whether a sample matrix contributes biasto the analytical results. The background concentrations of the analytesin the sample matrix are determined in a separate aliquot and themeasured values in the laboratory fortified matrix standards arecorrected for background concentrations. Laboratory fortified matrixduplicates are a second aliquot of the environmental sample used toprepare the laboratory fortified matrix standards. They are fortified,processed, and analyzed identically to the laboratory fortified matrixstandards. Laboratory fortified matrix duplicates are used instead of alaboratory duplicate to assess method precision when the occurrence oftarget analytes is low.

In some embodiments, a quality control sample is a solution of methodanalytes obtained from a source external to the laboratory and differentfrom the source of calibration standards. The quality control sample isused to verify the accuracy of the calibration standards.

Preserved reagent water is deionized water (resistance of 18.2 megaohmsor greater) wherein a preservative has been added. In one embodiment,preserved reagent includes the addition of approximately 200 mg ofammonium chloride per liter of deionized water.

As used herein, “fortified” indicates that the sample, standard, blank,etc. has the one or more target PFAS analytes added to the solution. Inother words, the sample, standard, blank, etc. that is “fortified” hashad the target analyte added in a specified amount to the fortifiedsample, standard, blank, etc.

Because the inventive method and system concerns PFAS detection at pptlevels, Teflon products are fastidiously excluded. If PFAS contaminationis unavoidable from the LC/MS/MS system, the detection of suchcontamination is not integrated or included in the determination ofconcentration and/or amount of the PFAS in question. The use of blanksallows detection of such contamination and correction is taken based onsuch detection. Blank subtraction is not a valid or acceptablecorrection for contamination.

A continuing calibration verification standard (CCV) is a calibrationstandard containing a specified concentration of method analytes, whichis analyzed at specified periods to verify the accuracy of the existingcalibration for said analytes. For some embodiments of the presentinvention, there is no substantially significant difference between alaboratory fortified blank and a continuing calibration verificationstandard.

A laboratory fortified matrix standard is an aliquot of an environmentalsample to which known quantities of method analytes are added in thelaboratory. The laboratory fortified matrix standard is analyzed like asample, and its purpose is to determine whether the sample matrixcontributes bias to the analytical results. The backgroundconcentrations of the analytes in the sample matrix should preferably bedetermined in a separate aliquot and the measured values in thelaboratory fortified matrix standard corrected for backgroundconcentrations. In various embodiments, a laboratory fortified matrixduplicate standard is a second aliquot of an environmental sample usedto prepare the laboratory fortified matrix standard. The laboratoryfortified matrix duplicate standard is fortified, processed, andanalyzed in the same way as the laboratory fortified matrix standard.The laboratory fortified matrix standard duplicate is used instead of alaboratory duplicate to assess method precision when the occurrence oftarget analytes is low.

Method blanks are aliquots of preserved reagent water that are treatedexactly as a sample including exposure to all glassware, equipment,solvents, reagents, etc. In various embodiments, the method blanks areused to determine if method analytes or other interferences are presentin the laboratory environment, the reagents, or the apparatus.

An internal standard is a pure compound added equally and in a knownamount to all standard solutions and samples. They are used to measurethe relative response of the method analyte. In some embodiments, theinternal standard includes isotopically labeled analogues (e.g., 13C) ofmethod analyte.

In some embodiments, an analysis batch is analyzed on the LC/MS/MSsystem. An analysis batch is a set of up to 20 field samples (notincluding quality control samples such as method blanks, continuingcalibration verification standards, laboratory fortified matrixstandards and laboratory fortified matrix duplicate standards) that areanalyzed on the same instrument during a 24-hour period that begins andends with the analysis of the appropriate continuing calibrationverification standard. In some embodiments, an additional continuingcalibration verification standard is analyzed after analysis of 10 fieldsamples.

Standards for initial calibration, ongoing calibration verification, andquality control samples, etc. are prepared by adding appropriate volumesof primary dilution standard solutions to preserved reagent water orsample. Primary dilution standard (PDS) solutions are solutions of oneor more method analytes prepared in the laboratory from stock standardsolutions and diluted as needed to prepare calibration solutions andother required analyte solutions. Stock standard solutions areconcentrated solutions containing one or more method analytes preparedin the laboratory using assayed reference materials or purchased ascertified from a reputable commercial source. For example, standards orother solutions of desired concentrations may be prepared from primarydilution standard solutions or a stock standard solutions if the desiredconcentrations are more dilute than the primary dilution standardsolutions or a stock standard solutions. Analogously, serial dilutionof, e.g., calibration standards of a given concentration, providecalibration standards lower and lower in concentration than the givenconcentration with every dilution.

Table 4 shows an example for the preparation of stock standard andprimary dilution standards.

TABLE 4 Stock Standards (SS) and Primary Dilution Standards (PDS)Example Preparation. Stock Standard Custom Mix-(SS) Primary dilutionStandards (PDS) Weight Volume Conc.⁵ Volume of Conc. Final VolumeStandard Analyte (g)³ (mL)⁴ (mg/mL) SS used (μL) (μg/mL) (mL)⁶ ID PFOS*¹0.0538 50.00 1.00 2.50 0.10 25.00 PDS 1 PFHxS*¹ 0.0548 1.00 2.50 PFBAPurchased as 0.0500 50.00 PFBS* solution of indicated 0.0442 57.00 PFDAconcentration. 0.0500 50.00 PFHpA 0.0500 50.00 PFHpS** 0.0476 52.0 PFHxA0.0500 50.00 PFNA 0.0500 50.00 PFPeS** 0.0469 53.00 PFOA 0.0500 50.00PFOS*¹ 0.0323 30.00 1.00 2.50 0.10 25.00 PDS 2 PFHxS*¹ 0.0329 1.00 PFBA0.0300 1.00 PFBS 1.00 PFDA 1.00 PFHxA 1.00 PFNA 1.00 PFHxA 1.00 PFOA***²Analytes purchased 0.0414 60.4 PFHpS** as solution of 0.0476 52.00PFPeS** indicated 0.0469 53.00 concentration. 13C- Analytes purchased0.05000 15.00 0.0075 100.00 IS PFHxA as solution of 13C- indicated PFDAconcentration. 13C-PFOA 13C-PFOS** 0.0478 15.70 *Potassium salt **Sodiumsalt ***Ammonium salt ¹Technical grade quantitative standards containingbranch and linear isomers ²Technical grade qualitative standardcontaining branch and linear isomers ³Analyte compound purchased neatfrom vendor. ⁴Weighed analyte dissolved with indicated volume ofmethanol. ⁵After dilution with methanol. ⁶After dilution with methanol.

Table 5 shows an example for the preparation of working standards.

TABLE 5 Example Preparation of Working Standards (WS). Volume of WSFinal WS Final PDS/ICS Volume Solvent Concentration WS Name Used (μL)(mL) Used (μg/L) ICS 6/CCV HL 250/PDS1 100.00 Preserved 0.25 ICS 5/CCVML100/PDS1 100.00 reagent 0.10 ICS 1/CCV LLa 100/ICS 5 5.00 water 0.0020ICS 2/CCV LLb 500/ICS 5 5.00 0.010 ICS 3 1250/ICS 5  5.00 0.025 ICS 42500/ICS 5  5.00 0.050 MDL a  50/ICS 5 5.00 0.0010 MDL b 250/ICS 5 5.000.0050 LFB ML 2500/ICS 5  5.00 0.050 (for DOC) QCS 50.0/PDS2  100.000.050 LFM/LFMD 50.0/PDS1  100.00 Sample 0.050 100.0 μL of IS is added to5.00 mL of each WS resulting in a concentration of 0.15 μg/L. ICS 1 isonly used for PFOS and PFOA. The RL for PFOS and PFOA is 0.0020 μg/L,the RL for all other compounds is 0.010 μg/L

In step 210, acceptable settings are determined for ESI massspectrometer conditions of individual PFAS analytes and mixtures thereofas described supra. An example of ESI mass spectrometer conditions isshown in Table 2 (supra).

In step 215, a chromatography gradient is developed that allows theanalysis of PFAS mixtures analyzed in the present invention. An exampleof a chromatography gradient suitable for separation and analysis ofPFAS mixtures is shown in Table 6.

TABLE 6 Example of an LC Gradient for PFAS Analysis of PFAS. LC GradientProgram for PFAS Analysis % 5 mM Ammonium Time (min) Acetate % Methanol0 85 15 1 85 15 3 5 95 5 5 95 5.1 85 15 6.6 85 15

In step 220 the chromatographic gradient developed in step 215 iscombined with the mass spectroscopy settings determined in step 210.Table 7 shows an example of triple quadrapole MS/MS method conditionsfor PFAS analysis after combination with the Table 6 LC gradient. Thechromatographic gradient and mass spectroscopy conditions must beoptimized to allow an appropriate number of scans across the peak. Toproduce good, reproducible peak shape and recoveries, a minimum of 10scans across the peak is required.

TABLE 7 Example of LC/MS/MS Method Conditions for PFAS Analysis. TripleQuadrupole MS/MS Method Conditions Retention Precursor Product CollisionCell Int Std Used Scan Time Ion Ion MS1 Frag Energy Acceleration forAnalyte Type (min) (m/z) (m/z)^(a) MS2 Voltage (ev)^(b) (V) QuantitationPFBA Primary 3.97 212.99 168.9 Unit 380 5 4 PFHxA 13C PFBS Primary 5.529298.99 98.8 Unit 380 37 1 PFOS 13C PFBS Qualifier 5.529 298.99 80 Unit380 41 1 PFDA Primary 6.068 512.99 468.9 Unit 380 9 3 PFDA 13C PFDAQualifier 6.068 512.99 218.9 Unit 380 17 3 PFDA Internal 6.068 514.99470.4 Unit 380 9 3 NA 13C Standard PFHpA Primary 5.815 362.99 318.8 Unit380 5 1 PFHxA 13C PFHpA Qualifier 5.815 362.99 168.9 Unit 380 17 1 PFHpSPrimary 5.905 448.99 98.7 Unit 380 45 1 PFOS 13C PFHpS Qualifier 5.905448.99 80.1 Unit 380 45 1 PFHxA Primary 5.686 312.99 268.9 Unit 380 5 2PFHxA 13C PFHxA Qualifier 5.686 312.99 119 Unit 380 21 2 PFHxA Internal5.686 314.99 270.1 Unit 380 5 2 NA 13C Standard PFHxS Primary 5.805398.99 98.9 Unit 380 41 2 PFOS 13C PFHxS Qualifier 5.805 398.99 79.9Unit 380 55 2 PFNA Primary 5.997 462.99 419.1 Unit 380 5 4 PFHxA 13CPFNA Qualifier 5.997 462.99 218.9 Unit 380 17 4 PFOA Primary 5.915412.99 368.9 Unit 380 4 4 PFOA 13C PFOA Qualifier 5.915 412.99 168.8Unit 380 17 4 PFOA Internal 5.848 414.99 370 Unit 380 5 4 NA 13CStandard PFOS Primary 5.987 498.99 98.8 Unit 380 45 2 PFOS 13C PFOSQualifier 5.987 498.99 79.9 Unit 380 55 2 PFOS Internal 5.987 502.9979.8 Unit 380 52 2 NA 13C Standard PFPeS Primary 5.694 348.99 98.8 Unit380 41 2 PFHxA 13C PFPeS Qualifier 5.694 348.99 79.9 Unit 380 41 2

For Table 7, the precursor ion is the deprotonated molecule ([M-H]−) ofthe target analyte. In MS/MS, the precursor ion is mass selected andfragmented by collisionally activated dissociation to producedistinctive product ions of smaller m/z. The product ion is one of thefragment ions produced in MS/MS by the collisionally activateddissociation of the precursor ion.

In the examples shown in Tables 6 and 7 the following instrumentation isused:

i) AGILENT LC/MS/MS System (Column: Analytical column ZORBAX ECLIPSEPLUS C18, 2.1×50 mm, 1.8 um);

ii) AGILENT 1290 INFINITY Autosampler;

iii) AGILENT 1290 Binary Pump;

iv) AGILENT 1290 TCC Column Compartment; and

v) AGILENT 6495 Mass Spectrometer.

In the examples shown in Tables 6 and 7 the data software used isAGILENT MASS HUNTER.

In step 225, a practical range of detection is determined usingcalibration standards prepared as described supra and method validationsamples. In these steps, quality control (QC) includes a demonstrationof capability (DOC) requirement, a determination of the method detectionlimit (MDL), and confirmation of the minimum reporting limit (MRL).

In various embodiments, an initial demonstration of capability (IDC) isperformed prior to analyzing any field samples and any time major methodmodifications are made. The following steps are exemplary:

i) Generate an acceptable instrument calibration and demonstrate a lowsystem background by analyzing an acceptable method blank. The massspectrometer is calibrated according to the manufacturer'srecommendations. Prior to the analysis of samples, the instrument'sperformance is optimized, and an instrument calibration curve isgenerated. The instrument is calibrated using standards at severalconcentrations. They are analyzed with every analytical run. Acalibration curve is generated for each analyte by plotting theresponses against known concentrations. In some embodiments, linearand/or quadratic regression models are used. Both weighted andunweighted models are used. In various embodiments, a calibration curveregression model and a range of calibration levels is used for allroutine sample analysis. The initial calibration is verified byanalyzing various concentrations of CCV ((low level) LL, (medium level)ML, (high level) HL) prior to sample analysis and after every 10 samples(see Table 5 supra).

ii) Analyze a method blank to demonstrate low background contamination.

iii) Demonstrate method precision and accuracy by analyzing 4 replicatesof a laboratory fortified method blank.

iv) Establish the method detection limit (MDL) by analyzing sevenreplicates of a laboratory fortified blank fortified at less than theconcentration of the reporting limits (RL) over a period of three days.The determination of the MDL is described in more detail infra.

Table 8 illustrates an example of a laboratory analytical run sequencefor this method, with QC parameters frequency, concentrations andacceptance criteria.

TABLE 8 Method Analysis Sequence with QC Frequency and AcceptanceCriteria. Sample QC and Instrument Calibration Anal # Name QCs, ICSs,CCVs Acceptance Criteria Frequency 1 ICS 1 1. Instrument Calibration isAnalyzed with every analytical 2 ICS 2 updated and recalculated againstrun. 3 ICS 3 the newly generated calibration 4 ICS 4 curve. 5 ICS 5 2.Each analyte in each 6 ICS 6 calibration point, except for theconcentrations ≤RL, must calculate to be ±30% of the true value. 3. Eachanalyte in calibration points at concentrations ≤RL must calculate to be±50% of the true value. 4. ICS 1 is only used for PFOS and PFOA. 7QCS 1. Recovery for target Analyzed after instrument analytes must be±30% calibration of the true value 8 MB 1. Must be free from Analyzedwith each batch of up to contamination that could prevent 20 samplesprocessed as a group the determination of any target within a workshift. analyte. Concentration of target analytes must be ≤1/3 RL. 9 CCVLLa 1. Recovery for PFOA and Analyzed at the beginning of an PFOS mustbe ± 50% of the true analytical batch of 20 samples value processed as agroup within a 10 CCV LLb 1. Recovery for target work shift. analytesmust be ±50% of the true value. 11 Sample 1* 12 LFM 1. LFM/D: Recoveryfor Analyzed with each batch 13 LFMD target analytes should be ±40% ofup to 20 samples 14 Sample 2* of the true value for all analytesprocessed as a group 15 Sample 3* except for PFOA and PFOS within a workshift. 16 Sample 4* should be ± 30% of the true 17 Sample 5* value f;precision as RPD should 18 Sample 6* be ≤30%. 19 Sample 7* 20 Sample 8*21 Sample 9* 22 Sample 10* 23 CCV ML 1. Recovery for target Analyzedwith each analytical analytes must be ±30% batch of up to 20 samplesafter the of the true value. first 10 samples. 24 Sample 11* 25 Sample1* 26 Sample 13* 27 Sample 14* 28 Sample 15* 29 Sample 16* 30 Sample 17*31 Sample 18* 32 Sample 19* 33 Sample 20* 34 CCV HL 1. Recovery fortarget Analyzed with each analytical analytes must be ±30% batch of upto 20 samples after the of the true value. second 10 samples. InternalStandard Response Relative Percent Deviation (ISRPD) must not exceed±50% for each analyte except PFDA. ISRPD for PFDA must not exceed ±60%*If sample contains a method analyte(s) at or above the MRL, analyze anassociated FB. If a method analyte(s) found in the field sample ispresent in the associated FB at a concentration greater than 1/3MRL,then the sample results are invalid.

An example of a demonstration of capability (DOC) study including thedemonstration of laboratory precision and accuracy are presented inTable 9 using 75 ∝L injection volumes:

TABLE 9 Example of a DOC Study for PFAS. Data File 17 18 19 20 AccuracyMethod's Precision Method's Amount Amount Recovered as Mean AccuracyStandard as Precision Analyte Added DEMO DEMO DEMO DEMO Mean RecoveryLimits Deviation RSD * Limits Name [μg/L] [μg/L] [μg/L] [μg/L] [μg/L][μg/L] [%] [%] [μg/L] [%] [%] PFBA 0.050 0.0524 0.0482 0.0478 0.04770.049 98.0 70.0-130.0 0.0023 4.6 <20.0 PFBS 0.050 0.0413 0.0452 0.04300.0434 0.043 86.5 70.0-130.0 0.0016 3.6 <20.0 PFHxA 0.050 0.0483 0.04950.0430 0.0454 0.047 93.1 70.0-130.0 0.0029 6.3 <20.0 PFPeS 0.050 0.05220.0472 0.0476 0.0506 0.049 98.8 70.0-130.0 0.0024 4.9 <20.0 PFHpA 0.0500.0542 0.0518 0.0468 0.0504 0.051 101.6 70.0-130.0 0.0031 6.1 <20.0PFHxS 0.050 0.0484 0.0504 0.0508 0.0482 0.049 98.9 70.0-130.0 0.0013 2.7<20.0 PFHpS 0.050 0.0522 0.0610 0.0584 0.0565 0.057 114.0 70.0-130.00.0037 6.5 <20.0 PFOA 0.050 0.0487 0.0542 0.0489 0.0502 0.050 101.070.0-130.0 0.0026 5.1 <20.0 PFOS 0.050 0.0491 0.0517 0.0546 0.0538 0.052104.6 70.0-130.0 0.0025 4.7 <20.0 PFNA 0.050 0.0616 0.0516 0.0517 0.05470.055 109.8 70.0-130.0 0.0047 8.5 <20.0 PFDA 0.050 0.0490 0.0539 0.04880.0535 0.051 102.6 70.0-130.0 0.0028 5.4 <20.0

Determination of MDL

MDL (Method Detection Limits) are the minimum concentration of asubstance that can be reported with 99% confidence that the measuredconcentration is distinguishable from Method Blank results. An exampleof a procedure for determining MDL is as follows:

First, an estimate is made of an initial MDL using one or more of: i) amean determined concentration plus three times the standard deviation ofa set of MB; ii) a concentration value that corresponds to an instrumentsignal/noise in the range of 3 to 5; iii) a concentration equivalent ofthree times the standard deviation of replicate instrumentalmeasurements of spiked blanks; iv) a region of the calibration wherethere is a significant change in sensitivity, such as a break in theslope of the calibration; v) an instrumental limitation; and vi) apreviously determined MDL.

Second, an initial MDL determination is made by selecting a spikinglevel, typically 2-10 times the estimated method detection limit fromabove, but less than the value of the laboratory established RL and lessthan or equal to a regulatory authority reported required detectionlimit (RDL), if one exists. Once the spiking level is determined, aminimum of seven laboratory standards in reagent water (containing allmethod preservatives, if applicable) are made at the selected spikinglevel concentration and they are processed through all steps of themethod. Generally, the standards used for the MDL are prepared in atleast three batches on three separate calendar dates and analyzed onthree separate calendar dates. Preparation and analysis may be performedon the same day. In general, statistical outlier removal procedures arenot used to remove data for the initial MDL determination since thetotal number of observations is small and the purpose of the MDLprocedure is to capture routine method variability. However, documentedinstances of gross failures (e.g., instrument malfunctions, mislabeledsamples, cracked vials) may be excluded from the calculations, providedthat at least seven spiked samples and seven method blanks areavailable. After the method is run, the spiking level is evaluated. Ifany result for any individual analyte from the spiked samples does notmeet a qualitative method identification criterion or does not provide anumerical result greater than zero, then the method is repeated withspiked samples at a higher concentration.

The method MDL is the greater of either an MDL based on spiked samples(MDLs) or an MDL based on method blanks (MDLb).

The MDL is calculated as shown below:

First, a mean of the measured concentration values X is calculated asshown below:

${X\text{?}} = {\text{?}{\sum{\text{?}\frac{Xi}{n}\begin{matrix} \\

\end{matrix}}}}$ ?indicates text missing or illegible when filed

-   -   Where:        -   i=from 1 to n;        -   n=the number of data points; and        -   Xi=the measured concentration value of an individual            laboratory standard.

Second, a mean percent recovery (R) is calculated as shown below:

$R = {\frac{X}{T} \times 100\%}$

-   -   Where:        -   X=mean of the measured concentration values; and        -   T=true concentration used.

Third, a standard deviation (Ss) is calculated as shown below:

${Ss} = \left. \sqrt{}\frac{\sum\left( {{Xi} - X} \right)^{2}}{n - 1} \right.$

-   -   Where:        -   i=from 1 to n        -   n=the number of data points;        -   Xi=the measured concentration value of an individual            laboratory standard; and        -   X=mean of the measured concentration values.

The MDLs is then calculated as shown below:

MDLs=t _((n−1,1−α=0.99)) *Ss

-   -   Where:        -   t_((n−1, 1−α=0.99))=the Student's t-value appropriate for a            single-tailed 99^(th) percentile t statistic and a standard            deviation        -   estimate within-1 degrees of freedom (see Table 10 below);        -   and        -   Ss=standard deviation of the replicate spiked sample            analyses.

For the MLDb, one of the following criterion is applied:

i) If none of the method blanks give numerical results for an individualanalyte, the MDLb does not apply and the MDLs is used. A numericalresult includes both positive and negative results, including resultsbelow a current MDL, but not results of “ND” (not detected) commonlyobserved when a peak is not present in chromatographic analysis;

ii) If some (but not all) of the method blanks for an individual analytegive numerical results, set the MDLb equal to the highest method blankresult; or

iii) If all of the method blanks for an individual analyte givenumerical results, then the MDLb is calculated as shown below:

First, a mean of the measured concentration values X is calculated asshown below:

$X = {\sum\frac{Xi}{n}}$

-   -   Where:        -   i=from 1 to n;        -   n=the number of data points; and        -   Xi=the measured concentration value of an individual MB.

Second, a standard deviation (Sb) is calculated as shown below:

${{Sb}\text{?}} = \left. \sqrt{}\frac{\sum\left( {{Xi} - X} \right)^{2}}{n - 1} \right.$?indicates text missing or illegible when filed

-   -   Where:        -   i=from 1 to n        -   n=the number of data points;        -   Xi=the measured concentration value of an individual MB; and        -   X=mean of the measured MB concentration values.

Third, the MDLb is then calculated as shown below:

MDLb=X+t _((n−1,1−α=0.99)) *Sb

-   -   Where:        -   X=mean of the MB results (zero is used in place of the mean            if the mean is negative);        -   t_((n−1, 1−α=0.99))=the Student's t-value appropriate for a            single-tailed 99^(th) percentile t statistic and a standard            deviation estimate within-1 degrees of freedom (see Table 8            below);        -   and        -   Sb=standard deviation of the MB analyses.

TABLE 10 Student's Single-Tailed 99^(th) Percentile t Statistic Values.Degrees Degrees Degrees Replicate of Student's Replicates of Student'sReplicates of Student's Number Freedom t- Value Number Freedom t-ValueNumber Freedom t-Value n n − 1 t_((n−1, 0.99)) n n − 1 t_((n−1, 0.99)) nn − 1 t_((n−1, 0.99)) 7 6 3.143 41 40 2.423 75 74 2.378 8 7 2.998 42 412.421 76 75 2.377 9 8 2.896 43 42 2.418 77 76 2.376 10 9 2.821 44 432.416 78 77 2.376 11 10 2.764 45 44 2.414 79 78 2.375 12 11 2.718 46 452.412 80 79 2.374 13 12 2.681 47 46 2.410 81 80 2.374 14 13 2.650 48 472.408 82 81 2.373 15 14 2.624 49 48 2.407 83 82 2.373 16 15 2.602 50 492.405 84 83 2.372 17 16 2.583 51 50 2.403 85 84 2.372 18 17 2.567 52 512.402 86 85 2.371 19 18 2.552 53 52 2.400 87 86 2.370 20 19 2.539 54 532.399 88 87 2.370 21 20 2.528 55 54 2.397 89 88 2.369 22 21 2.518 56 552.396 90 89 2.369 23 22 2.508 57 56 2.395 91 90 2.368 24 23 2.500 58 572.394 92 91 2.368 25 24 2.492 59 58 2.392 93 92 2.368 26 25 2.485 60 592.391 94 93 2.367 27 26 2.479 61 60 2.390 95 94 2.367 28 27 2.473 62 612.389 96 95 2.366 29 28 2.467 63 62 2.388 97 96 2.366 30 29 2.462 64 632.387 98 97 2.365 31 30 2.457 65 64 2.386 99 98 2.365 32 31 2.453 66 652.385 100 99 2.365 33 32 2.449 67 66 2.384 101 100 2.364 34 33 2.445 6867 2.383 ∞ ∞ 2.326 35 34 2.441 69 68 2.382 36 35 2.438 70 69 2.382 37 362.434 71 70 2.381 38 37 2.431 72 71 2.380 39 38 2.429 73 72 2.379 40 392.426 74 73 2.379

In general, an MDL verification is performed each time an MDL study isperformed and on an annual basis. In one scenario, if an MDL value isgreater than or equal to the concentration used for the MDL study, theconcentration used for MDL study will be the MDL verificationconcentration. In another scenario, if an MDL value is less than theconcentration used for MDL study, a laboratory standard is prepared andanalyzed in reagent water (with preservatives if applicable), whereinthe, laboratory standard prepared has an analyte concentration:

-   -   i) greater than or equal to the MDL value;    -   ii) no more than 2-3 times the MDL value;    -   iii) less than the concentration used for the MDL study and the        RL; and    -   iv) less than or equal to the RDL if applicable.

Determination of RL/MRL

The RL (or MRL) is established for each method/analyte using itscalculated MDL value. The RL/MRL is set at a value of 1 to 5 times theMDL value and then this set RL/MRL value is confirmed by processing andanalyzing seven replicates of laboratory fortified blanks (LFB) that arefortified with analyte at or below the set RL/MRL concentration. The LFBalso include all method-specified dechlorination agents (e.g., ammoniumchloride) and preservatives, which are included in typical samplepreparation.

First, the results of the analytical run are used to determine the meanconcentrations of the LFB and their standard deviations.

Second, the Half Range for the prediction interval of results (HRPIR)are calculated using the following equation:

HR _(PIR)=3.963×S

-   -   Where:        -   S=standard deviation of the seven LFB concentration            measurements; and 3.963 is the factor specific to seven            replicates.

An upper and lower limit of the Prediction Interval of Result(PIR=Mean±HR_(PIR)) provides confirmation of the set RL/MRL if it meetstwo criteria: The Upper PIR Limit (PIR_(UL)) must be ≤150% recovery andThe Lower PIR Limit (PIR_(LL)) must be ≥50% recovery for the RL/MRL tobe confirmed. The calculations for PIR_(UL) and PIR_(LL) are as follows:

${{PIR}_{UL} = {{\frac{{Mean} + {HP}_{PIR}}{{Fortified}{Concentration}} \times 100} \leq {150\%}}}{{PIR}_{LL} = {{\frac{{Mean} - {HP}_{PIR}}{{Fortified}{Concentration}} \times 100} \geq {50\%}}}$

In step 230, samples from various sources of water are collected andanalyzed using the above described method. For example, samples arecollected in 250 mL polypropylene bottles. In some cases, the 250 mLbottles are pre-charged with approximately 50 mg of ammonium chloride.

In an example for the analysis of PFAS in tap water, the water tap isallowed to run freely until the water temperature has stabilized, andthe flow is reduced to permit bottle filling without splashing. Thebottle is filled to the neck, taking care not to flush out the ammoniumchloride, if present. The bottle is then capped and agitated to dissolvethe ammonium chloride, if present, and placed in a cooler with frozengel packs.

In some cases, the samples received at the laboratory on the collectionday are transported in coolers with frozen gel packs and theirtemperature is maintained between 1° C. and 10° C. for the first 48hours.

In other cases, the samples that will not be received at the laboratoryon the day of collection are maintained at a temperature range betweenapproximately 1° C. to 6° C. until analysis is initiated at a receivinglaboratory. Typically, a maximum holding time from collection toanalysis is 14 days.

Samples are typically prepared for analysis by removing fromrefrigeration and allowing the samples to equilibrate to ambienttemperature. In most cases, the samples are checked for dechlorinationefficiency by testing with free chlorine strips to ensure that the freechlorine level is <0.1 mg/L. Samples, standards, and QCs are next loadedinto 2 mL autosampler vials. In some cases, the samples and QCs arespiked with 10 μL of an internal standard as described supra.

The samples are then analyzed by injection alongside the standards andQCs into an LC/MS/MS with ESI using the conditions described supra.

After the initial calibration is confirmed valid with the QCS and CCV,analyzing field and QC samples is typically begun at the frequencyoutlined in Table 8 (supra). The instrument's MASS HUNTER software isused in the calibration procedure.

MASS HUNTER analytical software uses peak areas and the internalstandard technique to calculate concentrations of the method analytes.Data may be fit with either a linear or quadratic regression withweighting if necessary. The calibration curve for PFOS and PFOA shouldbe forced through the origin. The percent recovery calculation for CCV,LFB, QCS and LFM is performed using the following formula:

${P = \frac{A - B}{T}} \times 100\%$

-   -   Where:    -   P=percent recovery;    -   A=measured concentration of analyte after spiking;    -   B=measured background concentration of analyte; and    -   T—true concentration of the spike.

Relative percent difference for the fortified matrix duplicate iscalculated using the following formula:

${\begin{matrix} \\ \\ \\

\end{matrix}{RPD}} = {\frac{❘{{LFM} - {LFMD}}❘}{\frac{{LFM} + {{LFMD}\text{?}}}{2}}X\text{?}100\%\begin{matrix} \\ \\ \\

\end{matrix}}$ ?indicates text missing or illegible when filed

-   -   Where:    -   RPD=relative percent difference;    -   LFM=measured concentration of analyte in the fortified sample;        and    -   LFMD=measured concentration of analyte in the fortified sample        duplicate.

Internal Standard Response Relative Percent Deviation (ISRPD) iscalculated as follows:

${ISRPD} = \frac{\begin{matrix}{{{IS}{Response}{in}{the}{Sample}} -} \\{{Average}{}{IS}{Response}{in}{the}{Initial}{Calibration}}\end{matrix}}{{Average}{IS}{Response}{in}{the}{Initial}{Calibration}}$

It should be appreciated that all combinations of the foregoingembodiments and additional embodiments discussed in greater detailherein (provided such embodiments are not mutually inconsistent) arecontemplated as being part of the inventive subject matter disclosedherein. In particular, all combinations of claimed subject matterappearing at the end of this disclosure are contemplated as being partof the inventive subject matter disclosed herein.

Although the invention has been described by reference to specificexamples, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the disclosure not be limited to thedescribed examples, but that it have the full scope defined by thelanguage of the following claims.

What is claimed is:
 1. A method for facilitating detecting PFAS analytesin a sample comprising: injecting a volume of the sample into anLC/MS/MS system that is configured to detect one or more PFAS analytesof formula C_(n)F_((2n+1))—X within the unconcentrated sample; wherein:the LC/MS/MS includes ESI; n is 3, 4, 5, 6, 7, 8 or 9; and —X is —SO₃H,—CO₂H, —SO₃ ⁻, or —CO₂ ⁻; subjecting the injected volume of the sampleto ESI conditions that include a sheath gas flow of approximately 8L/min to approximately 12 L/min; and detecting one or more PFAS analyteswithin the sample.
 2. The method of claim 1 further comprisingdetermining: i) a concentration of the at least one PFAS analyte withinthe sample that is at least approximately 0.010 μg/L; and/or ii) anamount of the at least one PFAS analyte within the injected volume ofthe sample that is at least approximately 7.5×10⁻⁷ μg.
 3. The method ofclaim 1, wherein the ESI conditions further comprise a sheath gas heatersetting of approximately 250° C. to approximately 400° C.
 4. The methodof claim 1, wherein the ESI conditions further comprise a probe gastemperature of approximately 120° C. to approximately 180° C.
 5. Themethod of claim 1, wherein the ESI conditions further comprise a gasflow setting of between approximately 11 L/min to approximately 20L/min.
 6. The method of claim 1, wherein the ESI conditions furthercomprise a capillary voltage setting of between approximately 1500 V toapproximately 4500 V.
 7. The method of claim 2, wherein the one or morePFAS analytes of formula C_(n)F_((2n+1))—X are chosen from: PFBA, PFBS,PFDA, PFHpA, PFHpS, PFHxA, PFHxS, PFNA, PFPeS, PFOA, and PFOS.
 8. Themethod of claim 1, wherein the PFAS analytes of formulaC_(n)F_((2n+1))—X are PFOA or PFOS.
 9. The method of claim 8, whereinone PFAS analyte of formula C_(n)F_((2n+1))—X is PFOA.
 10. The method ofclaim 8, wherein one PFAS analyte of formula C_(n)F_((2n+1))—X is PFOS.11. A PFAS analyte detection system comprising: an LC/MS/MS systemoperable utilizing ESI and configured to: receive an injected volume ofa sample containing one or more PFAS analytes of formulaC_(n)F_((2n+1))—X; wherein: n is 3, 4, 5, 6, 7, 8 or 9; and —X is —SO₃H,—CO₂H, —SO₃ ⁻, or —CO₂ ⁻; subject the injected volume of the sample toESI conditions that include a probe gas temperature of approximately120° C. to approximately 180° C.; and detect one or more PFAS analyteswithin the sample.
 12. The system of claim 11, wherein the LC/MS/MSsystem is configured to determine: i) a concentration of the at leastone PFAS analyte within the sample that is at least approximately 0.010μg/L; and/or ii) an amount of the at least one PFAS analyte within theinjected volume of the sample that is at least approximately 7.5×10⁻⁷μg.
 13. The system of claim 11, wherein the ESI conditions furthercomprise a sheath gas heater setting of approximately 250° C. toapproximately 400° C.
 14. The system of claim 11, wherein the ESIconditions further comprise a sheath gas flow of approximately 8 L/min.to approximately 12 L/min.
 15. The system of claim 11, wherein the ESIconditions further comprise a gas flow setting of between approximately11 L/min to approximately 20 L/min.
 16. The system of claim 11, whereinthe ESI conditions further comprise a capillary voltage setting ofapproximately 1500 V to approximately 4500 V.
 17. The system of claim11, wherein a detectable amount of PFAS analyte in a single receivedinjection of sample is at least approximately 1.5×10⁻⁷ μg.
 18. Thesystem of claim 11, wherein the one or more PFAS analytes of formulaC_(n)F_((2n+1))—X are chosen from: PFBA, PFBS, PFDA, PFHpA, PFHpS,PFHxA, PFHxS, PFNA, PFPeS, PFOA, and PFOS.
 19. The system of claim 11,wherein the PFAS analytes of formula C_(n)F_((2n+1))—X are PFOA or PFOS.20. The system of claim 19, wherein one PFAS of formulaC_(n)F_((2n+1))—X is PFOA.
 21. The system of claim 19, wherein one PFASof formula C_(n)F_((2n+1))—X is PFOS.
 22. A method for facilitating thedetection of PFAS analytes in a sample comprising: obtaining a samplecontaining one or more PFAS analytes of formula C_(n)F_((2n+1))—X;wherein: n is 3, 4, 5, 6, 7, 8 or 9; and —X is —SO₃H, —CO₂H, —SO₃ ⁻, or—CO₂ ⁻ receiving data representative of test results of an analysisdetecting at least one of the one or more PFAS analytes of formulaC_(n)F_((2n+1))—X within at least a portion of the sample, the testresults comprising one or both: i) the concentration of the at least onePFAS analyte in the sample; and ii) the amount within an injected volumeof the sample of the at least one PFAS analyte into an LC/MS/MS system;wherein: i) the concentration of the at least one PFAS analyte withinthe sample is between approximately 0.0020 μg/L and approximately 0.25μg/L; and/or ii) the amount of the at least one PFAS analyte within theinjected volume of the sample is between approximately 1.5×10⁻⁷ μg andapproximately 1.9×10⁻⁵ μg; wherein the analysis comprised the followingsteps a) and b): a) injecting a volume of the sample into the LC/MS/MSsystem with ESI that is configured to detect the at least one PFASanalyte; and b) subjecting the injected volume of the sample to ESIconditions that include a sheath gas flow of approximately 8 L/min toapproximately 12 L/min.